I was given an Dell Window XP Professional but it is locked and I do not know the password and the ex owner can't remember what it was. How do I unlock this computer?
If you don't have the Windows password you will need to reinstall the operating system. Windows XP is obsolete however and its reinstallation is not recommended.
What si the model of the Dell so we can determine Windows 10 compatibility?
Windows Vista is obsolete. Its time for you to install Windows 10 Insider 64 Bit Built 10030:
Use it as a stepping to get Windows 10 RTM. Microsoft's representative Gabriel Aul has stated that Microsoft will not cut Windows 10 Insiders off from reaching Windows 10 RTM.
Your question is very suspicious. It's easy to doubt the source of this computer,why did its former owner forget his password?but my dad forgot his administrator's password on his computer (He has a bad memory, Lololololo.........) Reinstall a clean system.Another ways : https://www.mobiledic.com/windows-topic/unlock-a-locked-windows-computer.html Without doing any reinstall for your laptop , all you need to is follow its steps .