It's for windows. But they are trying to raise money to pay someone to develop it for mac.
Hmm. I think that I would like it to be on Mac. I've used iPodWizard on Windows before. Its fun to use, and fun to see what you can find on its website to customize your iPod, and you feel a little special once its all done.
But it can get rather complicated to do some things(such as change your background on your iPod), and there's an inherent risk that you'll brick your iPod, that gets more and more likely the harder the thing you are trying to do is. But there isn't much risk in changing pictures(such as the battery icon or the Do Not Disconnect icon) and to change text in the iPod, which are my usual standbys.