Yeah you can do the updates with the oem version. Make sure you download sp1 or get a disc with it on. Here ya go, try this link:
Newegg.com - Operating Systems, Microsoft Windows Vista, Windows Vista 32, Microsoft Windows XP, Microsoft Windows Media Center, Linux
Look about halfway down the page and you'll see the Ultimate 64bit with the SP1 included. Looks like it's 20 bucks more. Only you can decide if it's worth $20 to just pop in the cd and let the installer do it's work or download the massive file and then install it after installing the original OS.
As to my system? Yeah I was too stupid to know I couldn't build it so just went ahead and did it. What I like is that I have room to upgrade to the 1600 MHz processors and RAM when they get down in price. Heck the 790 will take up to 2000MHz of SLI ready RAM (whatever that is. LOL by the time I decide to get it, I'll know.) I see they are working on an 8 core CPU, wonder if it will need a special Mobo? Just damn, I think I've picked a never ending "hobby.'' Looks like I'll never get my wood shop built now...........
EDIT: Oh. Here, have a beer.........