I'm planning on building my own PC with the help of a friend, and after reading through this article, it seems that I need to purchase a System Builder licence. Does this mean that I should not buy Windows 8 Pro for this pc, I should rather specifically buy the System Builder version?
As per Windows 8: The end of the full retail version?, Microsoft is no longer planning to sell full retail versions of Windows 8. Instead end users can now buy the upgrade versions and also the OEM/System Builder versions if they so choose.
Thus you can either buy:
Only #3 and 4 will really be of use for a new PC without a valid license for either XP/Vista/Windows 7. #1 and 2 can be clean installed as per this article, but you will initially need to use the Upgrade Assistant to qualify the PC, which means you'll need a valid genuine key for XP/Vista/Windows 7 at hand (plus according to reports the old OS does need to be installed as well).
In practice the 'system builder' or OEM version is simply a discounted version with less packaging, and no support. Its meant for sale with new PCs, and yes, you can install it on a new PC (and only a new PC as per licence).
Both are the same software sold through different retail channels - think of one as a 'wholesale' version and the other is 'retail' but they're both the same OS. You can get a System Builder Windows 8 professional copy or upgrade. The only change here is that previously you could not transfer a system builder licence between your own systems, now you can. This would not effect you in any way, and brings this licence in line with the retail licence
As this is a new build, the system builder licence would be a better choice since its lower cost, and you can get a professional edition with that licence.