Its an Antec Brand (quality), & there's more than enough amps to provide power to the vid card. (in a way you do combine the 3 rails, but it doesn't really come out to 18A x 3 = 54Amps, its usually less than the total... I think JP has a link or two that explains it better though)
As to the OEM, It used to be that you used to have to buy some major hardware components with the OEM disks, as I remember reading that the OEM versions of OS's were "tied" to that system & supposed to be non transferable to other systems, but that was something I read years ago...
But I think retailers had been letting that slide for years, as I remember reading & others telling me they've bought a simple PS/2 to USB adapter for a keyboard/mouse, with an OEM copy & was ok...
but anyways, a system builder also isn't exclusively like some name brand or aftermarket company, but there are thousands of Private system builders who do it for their own small business they run...
but, as to the GPU getting it at the same place, yes he could, but he'd be smart to do some comparison shopping at other sites as well, rather than everything at newegg... which was the reason I posted the one deal at Tigerdirect for the GTX...
And JP is right about the Clean install of the OS from an upgrade version... up until my purchase of WinXP Media Center Edition 2005 last year (OEM System Builders disk), thats all I've done (upgrade from a prior upgrade version), from Windows 3.11 to WinXP Home... Win 3.11 was just about the only full version I'd ever had, Win95b was an upgrade version, so was Win98, Win98SE, & WinME, then was WinXP Home (bought a 2nd copy of Home, & used a seperate Win9x upgrade disk as proof of purchase/ownership of prior OS to install with), I had a couple full OEM copies of Win98 & 98SE as well as Win2000 (snagged some sweet cheap deals on various forums over the years), but those were used soley for a couple of number crunchers for Distributed Computing projects.
but anyways, yes you can do a full clean install from an Upgrade version, just about the only difference between those & the Full versions is usually they require you to provide a prior version as proof that you can upgrade & install a full version anyways... in either case, you do a full install no matter what, or should/can do one...
but with a full version of the OS, at a deal like that, $90, its really worth it to just buy that & just go ahead & install it, with out having to dig around for a prior version, you'll normally spend about the same on an upgrade version anyways, which is why its such a good deal.