The high-end 9 series will come out in Feb-March as Dragon said.
There will also be high-end ATI (r700) cards coming out about the same time.
They should be the first 8800GTX killers in a long time.
Just get the 8800GT or 3870 if you need a card now. Get the 8800GTS 512 if you are planning on keeping that a long time or using the Step-Up.
If you don't care about speed, a 2600/8600 is good enough,.
Actually, I have a 8800GT I don't know much about the Step-Up. Link please! Thanks!