so it's fairly easy to import LemEdit levels across, for instance, as long as you have a hex editor. I've played several of the downloadable ones already this way, and I also played one I designed myself. It's actually really striking how much better the mac graphics are; I'd never realised it before.
Well yes, the Mac graphics are high-resolution. It should be similar to the ones you get when you play the Windows version in hi-res mode.
Beware though that the level might play slightly differently when you use the Mac instead of CustLemm:
1) Precision moves might be affected due to the use of high-resolution graphics on the Mac, while CustLemm uses low-res graphics.
2) Levels with tight time limits might be affected since on the Mac time goes slower (think "Just a Minute Part II").
3) CustLemm has a slightly extended fall distance of 66 instead of the usual 63 that the official Lemming (whether DOS, Windows, Mac, Amiga, etc.) uses. Very few levels are affected by this difference, but when it does affect the level, the difference can be significant (eg. geoopck1 #9).
4) Levels that depend on strange glitches or tricks will not necessarily work on the Mac, though I've found that many glitches do hold up on the Mac.