Have you read through the Rooting for Dummies guide? Try and download the drivers linked in the Rooting guide. You might also try and install then uninstall HTC Sync.
I read through the guide a few times before and note this is my second rooting exercise on an HTC device using unrevoked. I went back through the PC and deleted everything I could find (again), then installed and uninstalled HTC sync to be certain I had the right drivers for the EVO 4G. I just went back into properties (while plugged in using hBoot .97 set on "hboot usb plug". The device manager still says, "Unknown Device" and doesn't proceed when I tell it where the drivers are.
Stuck... I think I'm going to try this on my laptop so there are no previous "issues" from the Droid Incredible and see if it will work there. Stay tuned...
***Update*** Moved to a laptop that hasn't been connected before and got S-off via unrevoked...

