Personally, I wouldn't buy a new pc just to be able to play Bethesda's FO3. If it had been Van Buren, I would most probably have looked into upgrading mine, but Bethesda's FO3 is nowhere near the originals and you don't have to play it to discover that sad fact.
Wait for Diablo 3 to buy a new system, I have a feeling D3 will turn out well. And just be smart: wait a couple of months and before you know it, FO3 will be in the bargain bins for, meh, €15 or something like that. That seems to be a more justified price than the +€50 they charge for it right now. By that time, modding communities will perhaps have made it into an enjoyable experience for true Fallout fans. As it is now, it's just a simplified, dumbed down, over-commercialized, aimed-at-the-masses piece of epic fail.
My two bottlecaps.
-- alec