I wouldn't recommend doing that personally. Ideally, you want to clean the box, remove _all_ previous restore points and then set a new one once all is cleaned up.
Viruses / trojans / spyware etc "recently" have been using the system restore as another method of reinfection, plus it's unlikely Nathan knows _exactly_ when he got the first infection, so hard to know what maybe a clean restore point or a dirty one.
Regards,
Ian