Many free tools are available to detect rootkits. Some also attempt to remove them.
For some reason, free has become the normal price for anti-rootkit tools, and there's a new one now. AVG, the maker of security software products including the popular free AVG Anti-Virus, now has of it's own. The program supports Windows 2000 and Windows XP (32-bit) and does not provide any live protection, just scanning for and removal of rootkits.
Some other free Windows anti-rootkit tools:
Copyright 2007 by Ziff Davis Media, Distributed by United Press International