Well, I bit the bullet and spent £570 on a new machine with an Athlon 64-bit 3200+ processor. I'll need to buy another graphics card (it shipped with a Radeon Xpress 200 Series) and upgrade the 512MB RAM, but I'm satisfied that by release I'll have a good enough setup to play Oblivion.

I am now completely, miserably broke. Your move, Bethesda. :D