GFX card: When to buy?

I am planning to update my monitor and graphics card. I had hoped to get a 24" Samsung 245B and an 8800GT. Then I read about the 9800 and the next GX2 etc etc. So now I am a bit worried if I buy one something better will be out at a similar price point in a few months. It wouldn't bother me if the new €600 GTX came, as I couldn't afford that anyway.

So is it likely that the 8800 GT at €250 will be replaced in the next year?

I've read about 1gb versions of the GT. Some people said that they weren't worth it except for high resolutions, others that with a 256bit architecture they weren't worth it, period. The 24" Samsung is 1920 X 1200, is this a high resolution that would benefit or should I just stick to a 512mb?

Thanks for any help you can provide.