Is the computer actually acknowledging that there is a usb plugged into it? If its not appearing in my computer try typing in the search bar F:, E:,etc those would usually be the drives of a usb. I once used a computer that was recognizing that i plugged in a usb into it but they would appear in my computer unless i typed in the drive letter.
In xp i would remove any of attached devices then uninstall the usb ports,you could rescan but i prefer to restart then attempt to re-attach 1 by 1 ,ahhhhh the joys of external devices "D'oh" throws another comp on the computer pile :p
I know you said your "jumpdrives" don't show up anywhere but does anything else? i.e. digital camera,
It could be the usb drivers internally. You could also try contacting Microsoft and have them remotely connect to your computer and see what the problem is. Could be a driver and is everything currently updated?
One of the issues that i've read about thru cnet & TechRepublic is driver compatability in vista,it's actually not microsofts fault but is to do with hardware manufacturers,are you sure the units your attaching have any drivers for them to install into vista,not all USB devices work with what's supposed be standardised drivers
