On Mac OS X, even with XCode and command line developer tools installed, the SU installation of Ruby is not set up to enable compiling and installation of most C-library Gems. For example, one Gem I attempted assumed that there was an executable Ruby interpreter in the SU Ruby Framework where the Gem library lives (there is not - only the dynamic library loaded by SU). Fixing this requires loading a 32-bit Ruby compatible with SU, since the native installation is 64-bit. But even then the generated Makefile and other scripts fail due to problems with configuration. For example, Ruby was launched with an illegal command line option to one of the install scripts. In the end I hand-edited things and got the Gem to compile and install, only to discover as TT points out that SU's Ruby intentionally omits certain standard library components that were found to crash SU. Bottom line: with enough determination you can build a compiled-C Gem, but don't be surprised if libraries it wants are missing or if it BugSplats SU! Steve