Both Windows XP Full and Upgrade will upgrade your copy to Windows XP Pro. OEM will not. It is recommended you don't do an upgrade but instead do a clean install, but since you do not want to lose data, Windows XP Pro has the ability to upgrade. If you purchase an Upgrade copy instead of a full copy, you must upgrade you do not have a choice, there must be an OS already installed for it to work. That's the only difference.
John D. Saucier
jsauce@magicguild.com
Certified Technician
Network Administrator