Most of the time there is no difference between the OEM and retail version of the component. Another differnce I forgot to mention is that OEM components have a shorter warranty than the retail version. Other than that it's no point in saying OEM this and that. The only time it's important is for the processor, since the OEM version comes with the chip alone, while the retail version comes with a heatsink and fan. Hope that helps.
"A witty saying proves nothing." - Voltaire