Apologies for the triple post, it's been a little bit and I think if I edit my old post now, it will be missed.
It's down to
5600xt AGP 256mb (it's not PCI after all, I don't know why it was reading as such)
6200 plain AGP 256mb
From what I can find, I'm fairly sure the 5600xt will be the way to go, but I still haven't found any tests or benchmarks yet
I've read the 5600xt can play HL:2 and portal on fairly high settings and be fairly smooth, I hope this is true because I'd know exactly what card I'll be using.