The main question is how long do you want to wait? You can get a GF4TI4600 from Novatech for about £175 now, the GF FX will probably come down in price about 4-5 months after it comes out. Then the new one be GF???(6) will then be almost ready, and so you might end up waiting for that. You could end up waiting for the next one all the time.
Wait 3 months, there will be a better one along by then. Except for, after 3 months, there will be a better one due out in 3 months... and another one .... and another one - and so on.
Meanwhile, you just sat there wishing you had a better card than your ATI for £200. There will always be a better on 'real soon now' - the main reason manufacturers announce their product so far in advance is to stop you buying the competition's offering today.
If you have £200 now, and want to play games now, buy a card now. It would be commercial suicide for any game distributor to require an Nvidia FX (or ATI equivalent) within the next year - they need to maximise their sales.
That's not to say that the game won't run better with an FX, though :)