I'm assuming you want to add USB 2.0 on an older Mac here. Most PCI cards at retail stores don't say Mac-compatible on the box, but many name brand cards will work anyway. For example, my brother's Powermac G4 has a Linksys PCI wireless internet card and a PCI 5-port USB 2.0 card in there (sorry, I don't remember what brand it was, but I remember it was a name brand or I wouldn't have recommended it to him). Both of them were purchased at Wal-Mart, and neither even mentions Macs on the box, but both work perfectly. I'd just try a card and see, as long as you can return it if it doesn't work.