I helped a client of mine install VMware Server and used the following method to get his USB scanner (A Xerox 510) working. It worked with no problem, after getting the scanner installed. But he said that, for reasons not very clear to me, after encountering a paper jam, the scanner refused to work in Windows. I've uninstalled and reinstalled the latest drivers. It detects the scanner, but now always says that the device can't be recognized.

In the mean time, we're going to create a second VM and install Windows all over to see if that works, but in the mean time, I was looking for some other ideas of things to try.