I own a Dell XPS R-450 P2 128MB RAM. When I got the system it came with a Windows 98 cd. Is this the same as the retail version?. I heard that the Windows XP Upgrade will only work with retail versions, not OEM's!. Also would you buy the full version or just the upgrade. I may upgrade my system in the future with a new MOB-processor, and harddrive and will need to do a clean install, would it be better to get the full version or will the upgrade version work fine?. Thanks!.