My desktop (running Windows XP) just came down with a bad case of Cycbot.b -- anyone have good advice on how to deal with it?

That is NOT a trojan that you want.  Go here:
http://www.bleepingcomputer.com/forums/topic354181.html

and follow the instructions they suggest.
And I'd seriously suggest taking their advice to download what you need to then get your computer OFF the internet ASAP.
GL, it's not a pretty one.

Edit: and for future reference, having a copy of MWAB downloaded and tucked away somewhere safe will help in the long run.
It's a great program and does a great job cleaning up nasties like this one.

Thanks. I spent most of yesterday and this morning carefully retrieving my files from the computer, resetting all my passwords, and then to be absolutely safe reinstalling the OS and putting my computer back together. A real PITA.