Native Instruments’ software is already compatible with Mac OS X Leopard with some minor issues; the one significant issue was a problem with installers, and they’ve just corrected that:
Native Instruments Compatibility with Mac OS X 10.5 Leopard
Universal Installer Patch: direct download link
If you need to install NI software on a clean system — say, a machine you did a clean install on, or if you’re really lucky, a shiny, new MacBook Pro — this should make sure you’re in good shape.
Note there are still some bugs with NI software — be sure to read the whole guide. I’m not sure I’d jump into Leopard yet if I were a heavy user; I’d wait until a fix ships for some of the other issues.
Incidentally, as some people have asked, we’ll soon have a complete compatibility guide for Leopard and an ongoing guide to Windows Vista. And this time, we’re looking at making it editable so we can have even a small group of users keeping it up to date with more detailed information. Past coverage (worth checking comments on these, too):