How to reset my lenovo to factory setteings when someone installed windows xp on it?

You may still have the original software on a hidden recovery partition.

Press F11 while the computer is booting up. Here are the instructions. http://support.lenovo.com/...IGR-4VFUDU

Otherwise you'll need to order recovery disks from Lenovo.

Here try these…
http://zorin-os.com
http://robolinux.org

What was on it before? Your question does not help us much. Generally if the install was done properly using the official recovery disks for that model machine it should just restore as normal. If you do not have the recovery disk set you would need to boot from an original operating system disk or there might be a recovery partition on the machine. But if the operating system installed is not original there's NO recovery data to use. The install will have written over it. If you use a proper OS disk you will have trouble locating and installing the drivers, especially with Lenovo, their site is not good at finding you the correct drovers. And your cheapest option would be to buy the recovery disk set from them, as most manufacturers only charge the cost of media and postage. MUCH less tan an OS disk.

Unless it came with a restore disk (which i doubt it did) then you can't