I just had to plug in my Microsoft Optical Wheelmouse and it worked fine. I then installed the mouse software (Intellipoint). That actually disabled the touch pad settings for me, so I had to reinstall the touchpad software.
this is wierd. dunno if this applies to you. i got a intellimouse 3.0 usb mouse and when i plugged it in "slowly" it didn't detect it at all on all of the ports. but when i just pushed it in "fast" it worked. i'm not lying... truly wierd.