I need to change my OS from Vista Premium (from factory) to XP Pro ue to
software problems. Do I need to purchase the full XP Pro or can I just do an
upgrade?
Vista to XP is a downgrade, not an upgrade. Downgrades are never
supported.
You can either
1. Buy a Full retail or OEM version and do a clean installation.
2. If you own a previous qualifying version for XP (Windows 98, 98SE,
Me, or 2000), you can buy an Upgrade version of XP Professional and do
a clean installation with it, inserting the CD of the previous
qualifying version as proof of ownership when prompted to do so.
I almost always recommend against OEM versions, because they come with
several restrictions, the most severe of which is that they can never
legally be moved to another computer, even if the original one dies. I
recommend buying and doing a clean installation with the Upgrade
version. If you don't already have a previous qualifying version, you
should be able to buy a used copy of Windows 98 inexpensively.