This card has recently given up the ghost after only 18 months of ownership - is that normal?

Assuming it is, what would anyone suggest that I replace it with? I have seen this - XFX 8400GS 256MB nVidia PCI Express Graphics Card - I cannot tell if it is still compatible with my machine for one or whether it is an upgrade or downgrade?

upgrade for sure!looks like your old card is a PCI,and the new one is PCI-E[express]new technology ,does you board have pci-e slot.
check with the maker of the motherboard or you motherboard manual .

No I'm limited to pci only - does any one have a suggestion for the best pci card available?

Out of that list, I would've thought the ATi X1300 would be the best bet. If you could find a PCI version of that in full form then that would do you.

Or you could upgrade your motherboard and use a new card - but then you would probably have to change the CPU and RAM as well.