The Windows iPod will work flawlessly on the Mac. I just posted on a different thread about this same thing.
If you are buying an iPod I would suggest getting a Windows version for a couple of reasons:
1. You get MusicMatch Studio Plus for free.
2. You get a converter for the firewire cable to go from the (I'm not sure on the pins) big ones that Apple uses, to the little ones that some PCs use.
3. The only thing you need for it to work on the Mac is iTunes, which you can download for free from Apple's website.
4. Anytime you can get something for nothing, it's a good deal:-P
Due to the security to prevent file sharing on it, you can only sync it up with one computer at a time. So if you have 100 songs on your Mac and 400 songs on your PC and you want them all on your iPod you won't be able to do it unless you put all the songs on one computer.