Microsoft Knowledge Base Article 831829 contains the following summary:
This step-by-step article describes how System Restore in Microsoft Windows XP interacts with your virus scanning software. This article also describes how to remove infected files that you cannot clean from the System Restore data archive. As a result, you can continue to restore your computer to uncompromised restore points. This article also describes how you can revert to a previous infected restore point. This procedure is useful if you must restore an infected file.