I was setting up a new server for a client yesterday and was beating my head getting a few gems install.If you are having issues installing the ruby-xslt and ruby-xml gems on linux (I was on CentOS 5.1), make sure the developer libraries of libxml and xslt are installed. I had the rpms installed, but not the developer versions.

For Red Hat based builds, you can do the following:

yum install libxml2-devel

yum install xslt-devel

Then you can install the gems.

gem install libxml-ruby

gem install ruby-xslt

Here is what the failure looked like for gem install ruby-xslt:

gem install ruby-xslt
Building native extensions.  This could take a while...
ERROR:  Error installing ruby-xslt:
	ERROR: Failed to build gem native extension.

/usr/local/bin/ruby extconf.rb install ruby-xslt
checking for xmlParseDoc() in -lxml2... yes
checking for xsltParseStylesheetFile() in -lxslt... no
checking for exsltRegisterAll() in -lexslt... no
extconf.rb:4: command not found: xslt-config --cflags
creating extconf.h
creating Makefile
/usr/local/lib/ruby/1.8/mkmf.rb:1102: warning: global variable `$preload' not initialized

make
gcc -I. -I. -I/usr/local/lib/ruby/1.8/i686-linux -I. -DRUBY_EXTCONF_H=\"extconf.h\"  -fPIC -g -Wall -I/usr/include/libxml2  -g -O2 -DUSE_ERROR_HANDLER -DUSE_EXSLT  -c xslt_lib.c
In file included from xslt_lib.c:19:
xslt.h:36:27: error: libxslt/extra.h: No such file or directory
xslt.h:37:26: error: libxslt/xslt.h: No such file or directory
xslt.h:38:35: error: libxslt/xsltInternals.h: No such file or directory
xslt.h:39:31: error: libxslt/transform.h: No such file or directory
xslt.h:40:31: error: libxslt/xsltutils.h: No such file or directory
xslt.h:41:29: error: libxslt/imports.h: No such file or directory
xslt.h:44:30: error: libexslt/exslt.h: No such file or directory
In file included from xslt.h:52,
                 from xslt_lib.c:19:
parser.h:24: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘parse_xsl’
parser.h:25: error: expected ‘)’ before ‘xmlDocPtr’
In file included from xslt.h:54,
                 from xslt_lib.c:19:
extfunc.h:22:32: error: libxslt/extensions.h: No such file or directory
In file included from xslt_lib.c:19:
xslt.h:88: error: expected specifier-qualifier-list before ‘xsltStylesheetPtr’
xslt_lib.c: In function ‘ruby_xslt_free’:
xslt_lib.c:29: error: ‘RbTxslt’ has no member named ‘tParsedXslt’
xslt_lib.c:30: warning: implicit declaration of function ‘xsltFreeStylesheet’
xslt_lib.c:30: error: ‘RbTxslt’ has no member named ‘tParsedXslt’
xslt_lib.c: In function ‘ruby_xslt_mark’:
xslt_lib.c:53: error: ‘RbTxslt’ has no member named ‘xXmlResultCache’
xslt_lib.c:53: error: ‘RbTxslt’ has no member named ‘xXmlResultCache’
xslt_lib.c:55: error: ‘RbTxslt’ has no member named ‘pxParams’
xslt_lib.c:55: error: ‘RbTxslt’ has no member named ‘pxParams’
xslt_lib.c: In function ‘ruby_xslt_new’:
xslt_lib.c:80: error: ‘RbTxslt’ has no member named ‘tParsedXslt’
xslt_lib.c:82: error: ‘RbTxslt’ has no member named ‘iXmlResultType’
xslt_lib.c:83: error: ‘RbTxslt’ has no member named ‘xXmlResultCache’
xslt_lib.c:85: error: ‘RbTxslt’ has no member named ‘pxParams’
xslt_lib.c:86: error: ‘RbTxslt’ has no member named ‘iNbParams’
xslt_lib.c: In function ‘ruby_xslt_xml_obj_set’:
xslt_lib.c:136: error: ‘RbTxslt’ has no member named ‘iXmlResultType’
xslt_lib.c: In function ‘ruby_xslt_xsl_obj_set’:
xslt_lib.c:231: error: ‘RbTxslt’ has no member named ‘iXmlResultType’
xslt_lib.c:233: error: ‘RbTxslt’ has no member named ‘tParsedXslt’
xslt_lib.c:233: warning: implicit declaration of function ‘parse_xsl’
xslt_lib.c:234: error: ‘RbTxslt’ has no member named ‘tParsedXslt’
xslt_lib.c: In function ‘ruby_xslt_serve’:
xslt_lib.c:291: error: ‘RbTxslt’ has no member named ‘iXmlResultType’
xslt_lib.c:293: error: ‘RbTxslt’ has no member named ‘pxParams’
xslt_lib.c:296: error: ‘RbTxslt’ has no member named ‘iNbParams’
xslt_lib.c:297: error: ‘RbTxslt’ has no member named ‘iNbParams’
xslt_lib.c:299: error: ‘RbTxslt’ has no member named ‘iNbParams’
xslt_lib.c:300: error: ‘RbTxslt’ has no member named ‘pxParams’
xslt_lib.c:306: warning: implicit declaration of function ‘parse’
xslt_lib.c:306: error: ‘RbTxslt’ has no member named ‘tParsedXslt’
xslt_lib.c:306: warning: assignment makes pointer from integer without a cast
xslt_lib.c:308: error: ‘RbTxslt’ has no member named ‘xXmlResultCache’
xslt_lib.c:309: error: ‘RbTxslt’ has no member named ‘iXmlResultType’
xslt_lib.c:311: error: ‘RbTxslt’ has no member named ‘xXmlResultCache’
xslt_lib.c:312: error: ‘RbTxslt’ has no member named ‘iXmlResultType’
xslt_lib.c:315: error: ‘RbTxslt’ has no member named ‘xXmlResultCache’
xslt_lib.c:316: error: ‘RbTxslt’ has no member named ‘iXmlResultType’
xslt_lib.c:320: error: ‘RbTxslt’ has no member named ‘xXmlResultCache’
xslt_lib.c: In function ‘ruby_xslt_parameters_set’:
xslt_lib.c:425: error: ‘RbTxslt’ has no member named ‘pxParams’
xslt_lib.c:427: error: ‘RbTxslt’ has no member named ‘pxParams’
xslt_lib.c:428: error: ‘RbTxslt’ has no member named ‘iNbParams’
xslt_lib.c:429: error: ‘RbTxslt’ has no member named ‘iXmlResultType’
xslt_lib.c: In function ‘ruby_xslt_media_type’:
xslt_lib.c:453: error: ‘xsltStylesheetPtr’ undeclared (first use in this function)
xslt_lib.c:453: error: (Each undeclared identifier is reported only once
xslt_lib.c:453: error: for each function it appears in.)
xslt_lib.c:453: error: expected ‘;’ before ‘vXSLTSheet’
xslt_lib.c:457: error: ‘vXSLTSheet’ undeclared (first use in this function)
xslt_lib.c:457: error: ‘RbTxslt’ has no member named ‘tParsedXslt’
xslt_lib.c: In function ‘ruby_xslt_reg_function’:
xslt_lib.c:474: warning: implicit declaration of function ‘xsltRegisterExtModuleFunction’
xslt_lib.c: In function ‘ruby_xslt_to_s’:
xslt_lib.c:485: error: ‘xsltStylesheetPtr’ undeclared (first use in this function)
xslt_lib.c:485: error: expected ‘;’ before ‘vXSLTSheet’
xslt_lib.c:491: error: ‘vXSLTSheet’ undeclared (first use in this function)
xslt_lib.c:491: error: ‘RbTxslt’ has no member named ‘tParsedXslt’
xslt_lib.c: In function ‘Init_xslt_lib’:
xslt_lib.c:544: error: ‘xsltMaxDepth’ undeclared (first use in this function)
xslt_lib.c:545: error: ‘XSLT_MAX_SORT’ undeclared (first use in this function)
xslt_lib.c:546: error: ‘xsltEngineVersion’ undeclared (first use in this function)
xslt_lib.c:547: error: ‘xsltLibxsltVersion’ undeclared (first use in this function)
xslt_lib.c:548: error: ‘xsltLibxmlVersion’ undeclared (first use in this function)
xslt_lib.c:549: error: ‘XSLT_NAMESPACE’ undeclared (first use in this function)
xslt_lib.c:550: error: ‘XSLT_DEFAULT_VENDOR’ undeclared (first use in this function)
xslt_lib.c:551: error: ‘XSLT_DEFAULT_VERSION’ undeclared (first use in this function)
xslt_lib.c:552: error: ‘XSLT_DEFAULT_URL’ undeclared (first use in this function)
xslt_lib.c:553: error: ‘XSLT_LIBXSLT_NAMESPACE’ undeclared (first use in this function)
xslt_lib.c:554: error: ‘XSLT_NORM_SAXON_NAMESPACE’ undeclared (first use in this function)
xslt_lib.c:555: error: ‘XSLT_SAXON_NAMESPACE’ undeclared (first use in this function)
xslt_lib.c:556: error: ‘XSLT_XT_NAMESPACE’ undeclared (first use in this function)
xslt_lib.c:557: error: ‘XSLT_XALAN_NAMESPACE’ undeclared (first use in this function)
xslt_lib.c:584: warning: implicit declaration of function ‘xsltSetGenericErrorFunc’
xslt_lib.c:588: warning: implicit declaration of function ‘exsltRegisterAll’
make: *** [xslt_lib.o] Error 1

Gem files will remain installed in /usr/local/lib/ruby/gems/1.8/gems/ruby-xslt-0.9.5 for inspection.
Results logged to /usr/local/lib/ruby/gems/1.8/gems/ruby-xslt-0.9.5/ext/xslt_lib/gem_make.out