full retail box or OEM ver?

I am upgrading to windows xp,I have the hardware and software that xp requires my only concern is should i spend $300 on a retail fullbox version or buy one of the OEM version that is offered by a couple web merchants?.Am i safe and better of with the cheap oem ver or should I spend double
and buy the full retail ver.PLease note that i am aware that one come with support and the other not.