Pro pack is to upgrade from win8 basic to pro. Pro is to upgrade from xp, vista or 7 to 8. System builder (costs $100 but you still get $30 back) is to install on a system that does not match the above.

System builder: http://www.amazon.com/Windows-System-Builder-DVD-64-Bit/dp/B0094NY3R0/ref=sr_1_2?ie=UTF8&qid=1350673515&sr=8-2&keywords=system+builder

Note that for the pro and pro pack, you just need to buy it and you'll get the gift card automatically within a month. If you buy the system builder version, you have to enter gift card code WIN8SYST. That offer is only valid until october 25th, though.

Also, note that the above system builder is for win8 basic. Win8pro system builder is another $40.

They could have made this simpler....