I now have it working but for how long, I don't know. It has worked fine before, then suddenly quits working. This time, I removed all Intellipoint software, then re-installed the Windows Vista mouse driver and software (IP32Eng6.30.191.0) for my MS Wireless Mouse 2000 . I then shut down my computer , unplugged my MS Wireless Optical Desktop Receiver 2.1. I then started up my computer, and when the boot up process was completed, I plugged the receiver back in, MS installed the new hardware, and it has worked since. If it doesn't work, try re-bboting again. I did this before seeing the suggestion from davehc. This process makes sense as the receiver would have been using the original driver.
If this doesn't work for you, go to...