Anyway, I just wanted to thank everyone on this board for their help and advice, without which I never would have made it to this stage.
For anyone who remembers any of my posts and was wondering how things went, I'll list the parts I finally went with:
AMD X2 4600+
MSI K9N Neo-F
Corsair XMS2 2X1Gb PC26400
Antec Truepower Trio 550
WD Caviar SE AAJS 250Gb
Cooler Master Elite 330
Also got a very cheap Lite On DVD RW, which is louder than a [bleep] in heat, and will need to be replaced someday, but gets the job done.
Obviously it won't compare to some of the SLI-Twin-8800GTX-QX6800-PC28000-Double-chocolate-cream-fudge monsters some of you are sporting, but it's a huge step up for me, and so far I'm very pleased.