All PCI cards should work, I doubt it but it might only have PCI-X or that really old brown expansion, forgot the name, well old!
Some cheap RAM, P2s will be impossible to find these days, and probably not worth getting a new GPU as I guess the CPU will bottleneck everything. As said come back with £150 and try for a cheap ass PC, I am sure I made one for £120 ex. OS. Id did have a pen drive as HDD though