I have Webroot Antivirus with Spysweeper 5.8. Need help removing a rootkit!?

My anti-virus antispyware program keeps detecting "potentially rootkit masked registry" With the program mentioned above, I detect it, quarantine it, and then it disappears only to be discovered the next scan. It is detected running a custom scan, not a full scan. I recently downloaded the beta version of IE 8.2 and Media Player 11 replaced Media Player 10 when MS automatically pushed SP3 onto my system. I was wondering if that was the problem and the detection was a "false-positive." I restored my system prior to the downloads and got rid of IE 8.2 beta (still stuck with Media Player 11). I ran a custom scan and the rootkit didn't show up. Yea! Ran it again, and there it was, same as before. Webroot merely suggested I run two consecutive scans with the computer physically disconnected from the internet. Didn't work of course. Has anyone else encountered this problem? Is this a false-positive? Does anyone have any helpful suggestions on how best to proceed? Help! Much thanks.