This is partly, and maybe inconclusively, discussed just below in http://reviews.cnet.com/5208-6618-0.html?forumID=6&threadID=4877&start=0 (but for an external HD, not a cd/rw).
Assuming you have Windows 98 SE, you'd better invest some money in a USB2 PCI-card. It's much faster then a USB1.1 PCI-card. I assume the CD/RW will work with USB1.1 (it's compatible), but you'll find it too slow.
Kees
I want to get an external CD/RW. The one I want has a USB 2 cable. I have a USB socket. Is that O.K. or do I need a USB 2 socket?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic