http://www.sysinternals.com/ntw2k/freeware/rootkitreveal.shtml

RootkitRevealer is an advanced root kit detection utility. It runs on Windows NT 4 and higher and its output lists Registry and file system API discrepancies that may indicate the presence of a user-mode or kernel-mode rootkit. RootkitRevealer successfully detects all persistent rootkits published at www.rootkit.com, including AFX, Vanquish and HackerDefender (note: RootkitRevealer is not intended to detect rootkits like Fu that don't attempt to hide their files or registry keys).