Microsoft releases an updated version of the Windows Malicious Software Removal Tool on the second Tuesday of each month, and as needed in response to security threats.
The free tool searches for specific infections and is available through Microsoft Update, Windows Update and the Microsoft Download Center. Operating systems covered are Windows Vista, Windows XP, Windows 2000, and Windows Server 2003.
KB890830 64 bit version for Vista x64, Windows XP x64 and Windows 2003 x64 computers.
“Deployment of the Microsoft Windows Malicious Software Removal Tool in an enterprise environment”.
http://support.microsoft.com/kb/891716
MSRT is not a replacement for an anti-virus program, make sure you have one installed.
Microsoft® Malware Protection Center article by Oleg Petrovsky, Uprooting Win32/Rustock
Edit:
How to troubleshoot an error when you run the Microsoft Windows Malicious Software Removal Tool
http://support.microsoft.com/kb/891717
Rustock is a challenge to remove, if you experience difficulties try running MSRT in ‘Safe Mode’.
How to Start Vista in Safe Mode
Windowshelp-Microsoft
A description of the Safe Mode Boot options in Windows XP
http://support.microsoft.com/kb/315222
