As mentioned, SpyBot is great, then possibly the MS product (although manually review everything because I got a lot of false positives).

Then go here and download and play with these:
http://www.sysinternals.com/ntw2k/utilities.shtml

Filemon: Monitors file access. Play with the filtering to reduce the output.

Process Explorer: Excellent process monitoring tool.

TCPView: Basically tells you what processes are listening on ports and sending/receiving traffic.

Autoruns: Lists all entries in Windows where a process can automatically start up.

RootkitRevealer: Possibly try this, but it's probably not necessary for simple malware.

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Gareth