What would be cool would be if Propellerheads released the source code. They wouldn't lose any competitive advantage by doing so, and would stand to gain good will, while hackers with more time on their hands than Propellerheads would be able to update it (from getting it to run on OSX to porting it to new platforms, from Linux to hacked PSPs). And, of course, getting rid of the pointless CD check on startup.
Incidentally, the ISO image for the PC version isn't a pure ISO9660 image but has a large quantity of 0s at the start. If burning it with cdrecord (i.e., under Linux), you will need to first strip the nulls off with something like:
dd if=rebirth_pc_installation.iso of=rebirth.iso bs=4096 skip=75
There have since been more 303 emulators; there's a commercial VST/AU plugin here which is said to be good. And then there's Muon's Tau, a free-as-in-beer 303-esque softsynth. In the open-source world, there is a rather rudimentary open-source attempt at 303 emulation, written by Your Humble Narrator a few years ago, here (it runs on Linux and uses Curses).