mge456.
As far as I know, all of the Spybot immunisation is in the form of passive URL or domain name blocks, that would have nothing to do with a USB camera interface. Teatimer does monitor some processes and registry changes, but if it is not enabled then Spybot is not running until you start it. I have confirmed that the Canon problem I mentioned does occur even if Spybot is not installed, and also that the same camera will connect and download correctly on another XP SP3 computer which also has the same version of Spybot installed.
So if you turn off Teatimer and the problem remains, then you should look elsewhere, though for peace of mind it's not such a big job to un-immunise Spybot, uninstall it and if the problem is still there, reinstall it again.
From your description it sounds like the USB camera connection is probably being recognised, but the "event" mechanism is then not launching the next bit of software, usually a camera window or downloader that looks after pathing and naming of the photo files as they are downloaded. You might try to see whether when the camera is connected you can manually launch the camera window or downloader program (that works in the Canon setup).
Have you tried to obtain Vista specific drivers for the Nikon?
Has anyone mentioned this problem in relation to the Nikon on any of the camera forums.?
If all else fails, you could adopt the approach that many have taken when they have camera download problems, and simply remove the memory card and read it in a card reader.
Sorry I can't offer any more suggestions at the moment.