I take it you're still trying to compile an x86_64 system? =)
For cross compilation, try here: http://kegel.com/crosstool/
Make sure you read the documentation carefully. It's all there. Hell, it'll even make you a true canadian-cross if you want it to!
For x86 --> x86_64 try here:
I'm 90% sure that's the page that finally got my system running on a 64-bit kernel *and* that had a fully native 64-bit toolchain. I ballsed up somewhere after getting it running, however, which is why I moved on to Slamd64 (see here: http://www.kaear.co.uk/projectdisp.asp?ID=59
), but in theory it'll work.
Typically I read this board at work without my home favourites - so I'm always forgetting the links I've used in the past (that are stored at home).
Don't forget to apply the right patches for the toolchain you're building, and also, be aware that the native toolchain (the versions) you're using to build with will affect what version of new toolchain you can build.