There's a gcc3 toolchain available at
http://handhelds.org/download/toolchain/osx/ . Personally, I just made a symlink from /opt/cross to the mounted disk image, as it has to be on a case sensitive filesystem, which a disk image is convenient for. In addition, if you decide to try the OE system,
http://openembedded.org/oe_wiki/index.php/...ildrootOnMacOSX is quite helpful. The above toolchain seems to work fine with OE.
I'm currently struggling with OE; having some problems getting qt compiled (or some tool in it's code, rather; I forget what exactly) - it fails with some errors to do with qpsprinter.cpp and stuff. Only progress I've made is, I think, you need to replace the #include of qt_X11.h with an include of <X11/Xlib.h> - or perhaps find a qt_X11.h, not sure, I'm just bumbling my way along, heh.
Good luck! Hopefully you'll get it working!