Yeah MS makes things a bit confusing --- the OEM version is technically for installing on a single system built by someone for resale to someone else (IT is actually not supposed to be used for a system you build for yourself - though most of the time this is what is done with them)
So technically you should not be using an OEM license but it will work just fine for what you are doing.
2nd the Upgrade version is for an existing system that you are changing so again technically you should not use it for an old HDD you are bringing to a new system but again it will in most cases work fine. Alsp it depends on what version of XP you had (IF it was an OEM version then technically the license expires with the MOBO of the old system and should not be used to upgrade a new system.)
So in summary --
To be completely in line with the EULA and License you should be buying a retail version of the OS --- but that said purchasing either an OEM or Upgrade version will usually work and activate fine since the OEM versions are sold by companies to be used for building new systems and the Upgrade media merely runs a check to see if certain files from an old version are present on the HDD which are there. So the answer to your question is it will work but will technically be a violation of their EULA so whether to do it or not depends on you.