If the key issues are using PowerPoint, plugging into projectors and hooking up to various internet connections, you should have very little trouble with a Mac PowerBook. To go further, there is really nothing significant I know of that can be done on Windows but not on Mac OS. The only issue I can think of that comes up sometimes is that someone will suggest you use XYZ application to do something, and you may have to come up with ABC substitute application because XYZ is only for Windows. But I've never had trouble finding such a substitute. And even then if all else fails, you can use Virtual PC to run Windows on your Mac.

At work we use Macs anyway, but I'm confident that I could get by in most Windows environments with only a Mac.