using USB devices with my CC

If you've done a full install of 8.1, it should have the appropriate drivers installed.

Do you know if the card is actually Mac compatible?

I seem to recall a list of compatible cards being posted somewhere, but a quick Google search met with failure. I may be thinking of wireless cards...

The USB support in 8.1 is pretty sketchy, and was mostly tailored to work with the built-in ports on the original iMac and Blue-and-White G3. Most devices and third-party USB cards require the "USB Adapter Card Support 1.4.1" package which only runs on 8.6 or better.

http://docs.info.apple.com/article.html?artnum=31132

Here's a mailing list thread on the subject:

http://ls.berkeley.edu/mail/magnet/2001/0439.html

--Peace

I haven't heard about it.

An abbreviation:
MoBo = MotherBoard.