I would highly recommend you don't try try this yourself :) Originally I planned to write a little note on how to do it, but after about the third hour I'd forgotten what I'd hacked to get to the point I was at. If you do try, don't bother with gcc-3.4; it has some sort of heisenbug that segfaults the assembler in various ways. And just getting C and not g++/ada/pascal/java/etc was also harder than it should be.
Anyway, with the packages installed you need to build the kernel with two extra flags.
$ make CROSS_COMPILE=i386-linux- ARCH=i386
Other than that, the built binary boots fine for me in qemu on my iBook!
update: If you want to compile userspace apps, you will need to use tpkg-install-libc from toolchain-source.