You're right. the chances of two cards have the same problem is very unlikely to be the hardware.
Just to rule out the possibility that some OS (mis-)configuration is the problem you could try to load a Linux Live CD and see if it works from there.
I know that ubuntu 9.04 was just released last week so that may have integrated drivers but i also found some threads on the ubuntu forums. Since its a live cd, just reboot to get back to normal windows.