I downloaded both rndis drivers available from the archive, none worked with the official usb cable supplied with the GP2x. After I used the usb cable for my camera and connected it, the GP2x was immediately recognized on my computer and was installed.
However, there are still problems since I can't even copy and paste files over the memory stick via the GP2x without a copy sector error. I have to go back and use my flashcard reader. I may also try installing the rndis drivers now that it detects the GP2x, maybe that'll fix the copy sector errors.