I've added a patchfile to the http://www.rockbox.org/twiki/bin/view/Main/UiSimulator page (at the bottom) which patches the CVS sources so that they build and run on Mac OS X 10.4.6 with gcc 4.0.1. Someone probably wants to add them to the source tree at some point before they get too stale.
They involve patching "tools/configure" to add a simulator case for Darwin, patching the "apps" Makefiles to use "-dynamiclib -Wl,-single_module" instead of "-shared" on Darwin, and patching "uisimulator/common/io.c" to handle the Darwin case much like the FreeBSD case. There are still issues (running on a dual 2GH G5 Powermac): * sound plays in bursts, and the debug output keeps signaling "sdl_audio_callback: No Data." * the JPEG viewer bus-errors and crashes the simulator: Fatal signal: Bus Error (SDL Parachute Deployed) 2006-05-10 20:49:50.356 rockboxui[7509] *** _NSAutoreleaseNoPool(): Object 0x318ce40 of class NSCFArray autoreleased with no pool in place - just leaking ...[another six or seven of those]... I can view text files, and play most of the games. I've only tested it with the iPod video simulator. Bill