I wanted a native x86_64 toolchain for kernel compiles so I downloaded the CodeSourcery src packages. They had a script that was good but it is really written for their internal use. I modified the script so it works, added variables to control the build process and stripped out the "internal" parts.
Most people should be able to download the script and just run it (It take about 3Gigs of available disk space in /var/tmp to run). It would be interesting to know if Apple users can get it to work (of course gcc and binutils have to be installed).
I've built the tools on i686 and x86_64 and have compiled a working kernel with x86_64. It seems to work fine.http://sheeva.with-linux.com/sheeva/tools/BuildCodeSourcery-Arm2009Q3-68.sh