Thanks very much indeed for the advice - very kind of you to help out with what I realise is essentially a bone question! Thought I would seek the advice of those more experienced in these things first tho.... it's the first time I've ever fiddled with a graphics card, so it's new territory for me.
I'm toying with the idea of a 400W PSU; do you reckon that's going to be enough? I've read about a lot of these cards needing around 70 - 100W, so I reckon that'd do it?