Well, that took longer than I thought it would, but I've finally reinstalled everything, and I've still got the problem, so I'm sending this bl**dy card back.
After I installed my mobo drivers, I started getting odd red line effects all over the screen untill I installed ATI drivers, and the crashing problem is still with me, so I'm going to return it as faulty and try a different card altogether.
I'm going to go back to nVidia, methinks. Would anyone recommend a particular one to me, that has DVI and 256M for roughly a £35-40 price tag?