Trojan.Zeroaccess!inf won't go away! Please help!!

Norton Internet Security found that my c:\windows\system32\services.exe file is infected with Trojan.Zeroaccess!inf and needs to be manually removed.  I've tried the recommended removal tool twice (once in Safe Mode), but after a full system scan, it's still there.  Please help!  I'm running Windows 7 64-bit.  Thanks!!