Typically, rootkits act to obscure their presence on the system through subversion or evasion of standard operating system security scan and surveillance mechanisms. Often they are Trojans as well, fooling users into believing the rootkit is something else, something which they expect will be safe to install and run on their computer system.
Microsoft's Rootkit Revealer program can be downloaded here: http://technet.microsoft.com/en-us/sysinternals/bb897445.aspx
OK, so you're probably not going to believe me, and you're going to select someone who suggests some other anti malware program to clean your computer as the best answer. But then you'll realize that it didn't work, and you're still looking for a solution, THEN read this:
I've been a network administrator for over 12 years now. Here's what I do about virus and spyware infections: I backup all the documents, pictures, music, etc., and then I put in the Windows CD and have it format the hard drive and start over. That's the only way to be 100% sure that all of the infections are removed. For backing up the data files, I prefer an online file host (such as http://www.drivehq.com ) instead of a USB drive because recent viruses (like Conflicker) can infect your USB drive.
What should you back up? Almost always these days, if you just back up your "My Documents" folder (and the My Documents folders for other users on the computer), you'll have saved everything. Microsoft and third party software manufacturers are becoming very good at making sure all of your stuff goes into that folder, or a subfolder (such as My Pictures).
For the future, I recommend that you use Mozy Home Free Edition to keep your documents backed up online. Then you won't have to hesitate if you want to ever reformat your computer again. Here is a YouTube video that I made about how to use Mozy: http://www.youtube.com/watch?v=RmhAoPCmOdY
I also recommend installing Site Advisor at http://www.siteadvisor.com. It will pop up a red balloon any time you go to a web site that has malicious downloads. It will also put red, yellow, and green icons next to your Google and Yahoo search results.
I've been getting into Comodo lately: http://antivirus.comodo.com/
Actually, I don't know how well the anti-virus component of it works, but the thing is this: it has a "sandbox" feature. Unless you specifically tell Comodo to allow permanent changes, everything that you do in your browser gets undone when you restart your computer.
Here is a Hak5 podcast that showcases Comodo's sandbox feature: http://www.hak5.org/episodes/episode-703