Hi Derek185,
I'm unsure if I understand your question. If you don't have a Valid Product, you would not be able to Reinstall untill you get a Valid Product Key.
However, If you get a Valid Product Key, you do not necessarily need to Reinstall to use it. You could, instead, change out the bad key with the Valid key using the Product Key Update Tool
http://www.microsoft.com/genuine/selfhelp/XPPkuinst.aspx?displaylang=en&sGuid=f4f86856-4250-45cf-94ef-1659e3859b42Note: If the Product Key Update Tool fails to change out the Product Keys then that usually means that the XP is a non-standard install, so to use the Valid Product Key, you would need to reinstall XP using the Valid key.
Hope that answered your question,
Darin MS