Eclipse will run MCC18, with help of the CDT. If you use a makefile, stock will do. FIRSTclipse provides plugins for managed make. The error parser won't work on non-windows, though, since it doesn't do any path translation.
Running MCC18, though, is slightly more challenging. (Disclaimer: I don't own a mac, so this is gathered.)
He's the scenarios I've found from reading:
- PPC: Good luck. No native/inline emulators seem to be available.
- Mac OS X86: It's BSD Unix. Use wine (or some variant) and follow the Linux instructions
- Bootcamp: Load windows, handle everything normally.
A more pressing problem with Mac may be the lack of RS-232. OS X can handle USB-Serial adaptors, IIRC. Classic Mac might have problems, since Apple used its own spec which is not pin-compatible with RS-232.