How do I reinstall/uninstall drivers from Windows Update

For some reason Vista lost my driver updates from WU and now the hardware is
showing up as unknown devices. Driver updates do NOT show up under
"Installed updates" anywhere. But they do show up in the install history.
How can I uninstall these and re-install them? Or how can I trick WU into
thinking I haven't installed these updates yet? Is there a way of manually
uninstalling the drivers?

As I said, the devices are now unknown devices (HDTV Wonder). So there is
no way to uninstall them from Computer Management's Device Manager.

After installing Windows Vista, the driver problems have now appeared in my
Windows XP installation.