OEM XP is the full version. I use always use it in the machines I build. I always us XP Pro. The extra cost in the OEM version is small and there are some advantages in the Pro version.
The things supplied with many commercial machines are "recovery disks" which help you "recover" the operating system from a hidden partition on the hard drive. Or they are part systems merely to enable you to get you machine going again but which would not be capable of installing the operating system themselves.
Quite often nowadays though, you don't even get that.
The important thing with OEM XP (Home or Pro) is that you get no Microsoft support with it. If you think you will need that, go for a retail version. (Or you can always come the the Helproom here!!!!)