Well, I think the answer is pretty clear actually, but to make it definitive...
GET THE RADEON x1950PRO!!!
1. It has outstanding performance considering the price
2. IMHO there is no point spending any more when you'll no doubt want to get a DX10 card in the next 12 months or so.
3. I know I'm ATI biased, but for the price range it is the best on nearly every benchmark.
If you have to spend a little bit more, get the Radeon x1950 XT which is about £175 and a bit faster.