yeah I would dl the updates before dropping a few bills on a cpu. If your worried bout the updates and not useing a cd, by now there should be a no cd crack that works.
I never like using my cd because taking them in and out scratches them and some games the game runs faser with out the cd, (thought that wasnt a prob anymore?) But most the time I just image the game disk and mount it to avoid f-ing up my $50.00 game disk. I need to learn to handle disks better, but Im lazy, throw them hear, there, $50.00 coaster on the coffee table over in the living room, yeah not good.
as for memtest not working I dont know, but maybe you could bring up the task manager to see if you got 2gb, it may still be bad even if it shows up as 2gb but if you get 1gb showing you know thats a prob.