Volume and Eject Keys No Longer Work After Boot Camp 2.1 Update

Earlier this evening I allowed the Apple Software Update app in Windows to update Boot Camp to version 2.1. I allowed the computer to restart following a successful installation of the update. I've restarted two more times since then. Ever since the update (including before the computer restarted for the first time following the update), the volume and eject keys on my keyboard don't work. I also have an Apple Wireless Keyboard (one of the 2003-2007 era white/clear ones) and it exhibits the same problem. Both keyboards otherwise work fine. The computer also otherwise works fine, and there's no evidence of any driver problems.

Some other potentially relevant information:
1- The Boot Camp icon is no longer present in the Windows System Tray.
2- The Boot Camp Control Panel is still present in the Windows Control Panel and it works fine.
3- All settings in the Boot Camp Control panel are unchanged from their defaults. In particular, I have confirmed that "Use all F1, F2, etc. keys as standard function keys" is still unchecked.
4- The Windows Device Manager properly recognizes both keyboards as Apple Keyboards.

I'm using Windows Vista Ultimate on an early 2008 MacBook; system specs are in my signature. Any ideas?

Thanks for taking the time to read this, and double-thanks if you can respond with any suggestions!