Windows XP upgrade over OEM version of XP?

Can a Windows XP upgrade version be used to upgrade an OEM version of XP?
I know this sounds strange but let me explain what I want to do. I have an OEM computer that came with XP. I had to replace the motherboard and power supply and after it didn’t want to let me activate XP. After trying several times for some reason it let me activate it. I’m afraid if I have to reinstall it again it won’t let me activate it again. Since Office Depot has Windows XP upgrade for $30 after rebate I thought this might be the cheapest way to solve this problem by getting a new serial number.

If it won't let you install just call MS and explain you had to replace the motherboard. If you want to upgrade you can upgrade from XP Home to XP Pro. I don't think you can upgrade from an OEM XP Home to Upgrade XP Home. It is still XP Home.

Yea, I called MS and they said that since the motherboard had been changed it was no longer considered A "E-Machines" computer and to call E-Machine. They wanted $20 just to talk to them so I figured it wasn't worth the gamble to have them tell me I had to buy another version of Windows.