The oem versions are only $10 difference on NE. I've got an old HD with a valid licensed copy of XP. I'm thinking that may work since I'll be adding the DVD software and most all other apps. The retail upgrade versions cost more than the full OEM version that is why I'm considering those. I will being a PC some but I have a great PC already in the house, so this one will mainly be used as an HTPC. I'm anxious to try Vista, but don't want to spend the money if I don't need to.