chances are if you never actually got a cd then its OEM you will need. It does not matter which version of home you source as long as its OEM as you can slipstream service packs and create a unnattended install using
nlite.This info of course in incorrect if the pc has media centre edition installed but as theres only one version (OEM) of this then you cant go wrong in your sourcing.Please note media centre is on 2 cds when promted for service pack cd then you add disc 2 this is a wonderful mistake by M$