Zip files are just a compressed collection of files and they are fully compatible with OS X. Whats inside the zip file may not be compatible, but the zip can be opened/extracted in OS X.
I do this all the time when I transfer files between my PC and Mac.
I am a paid user of ZipIt and have never had a problem with it. Mostly, however, I use the Stuffit Deluxe suite. I have not yet gotten around to checking out Apple's built-in ZIP utility. There have been a lot of catawauling on forums like this one that Jaguar's built-in ZIP is incompatible with Windows-based ZIP. There are a lot of children around here who cry "Wolf!" Until I have the opportunity to test Apple's ZIP myself, I will reserve judgment.