xp !!Initiating a recovery from the hard drive recovery partition
To initiate a recovery from the hard drive recovery partition, follow these steps:
1. Back up all personal files.
2. Restart the computer, and then press f11 before the Windows operating system loads.
3. Click a recovery option, and then click Next.
4. Follow the on-screen instructions.
same on vista
this should put it back to the factory settings ie when you first bought it will delect all virus's please dont shoot me if it doesnt work i got it from the hp website
HP Compaq 6720s Notebook PC
Maintenance and Service