yeah your right, keeping the outdated agp pc running would be wasting your money.
Talking about wasting money, first off that card is alot cheaper on Ebuyer
http://www.ebuyer.com/UK/product/126408
So maybe the other parts will be cheaper too? i havent looked.
I was going to surgest getting a 7900 instead since there around the same price as the xfx7600GT on Novatech, but then i realised the clock speeds on that Fatal1ty card are more than the standard 7900 what with it being pre-overclocked as standard

£82 for that is a bargain and it looks alot nicer than the normal 7600's