OEM is no different in terms of authentication then a retail version. Only difference is that OEM version will not aloow you to upgrade.
From:
http://www.helpwithwindows.com/WindowsXP/activation.html
Reinstallation of Windows XP on the same or similar hardware and a subsequent reactivation can be accomplished an infinite number of times. Finally, the Microsoft activation clearinghouse system will automatically allow activation to occur over the Internet four times in one year on substantially different hardware. Every 120 days, the current configuration of a user's PC will become the new "base," so to speak. This means (for example) that on a non-dockable PC you could change 8 of the above parts without a reactivation. After 120 days, you could again change 8 parts. This last feature was implemented to allow even the most savvy power users to make
changes to their systems and, if they must reactivate, do so over the Internet rather than necessitating a telephone call.
From another post I made on the subject:
There is only one Windows XP Pro distribution. There is one thing different in one file, which is a 5+3 number combination in I386/setupp.ini under the Pid= field
The first 5 digits inform setup what kind of install to allow. Examples:
51882 = Retail setup (allows upgrades or new installs)
82503 = OEM setup (allow new installs only)
The last 3 digits inform setup what kind of CD keys to accept
335 = Retail (accepts retail keys during setup)
270 = VLK (accepts Volume Licensing Keys, which some people here are calling corporate edition keys)
OEM = OEM (accepts OEM keys)
Normally retail cd numbers are matched with retail keys and so forth, but you can also mix and match, say if you wanted to create your own super slipstreamed XP disc that would accept your Dell OEM CD key for when you upgrade the hard drive on that Dell.
Often OEM installs will include additional drivers, or extra setup tasks, or different default wallpaper, but that's all.
.
