9600GT should be able to play new games for a very long time. most new games coming out have a dx10 and dx9 mode so you can play with older cards, as such eventually they will start coming out with dx11/dx10 games (Dirt 2 for example). You will still be able to play those games, you just wont get the benifits/shiny goodness of dx11. you will start getting out of luck when dx12/11 games come out, but thats many many years from now.
do you already have the 9600gt or are you thinking about buying a 9600gt because there are better options that you could get for roughly the same price. The aTi 5670 will offer roughly 15% -20% better performance for about 10 bucks more and dx 11 support.
Now if you already have that 9600gt on whatever setup you have, you won't be able to use play dx 11 games, But as of now, only a hand full of games, use dx 11 like P1n3apqlExpr3ss even those that do support dx 11 also support either dx 9 or dx 10 which your 9600 gt does support
Even better! I was only trying to make a point that you can still use older games because the creators of the game made it able to run off of multiple DX versions, thus allowing older cards to be able to play them.
K guys, no kidding... ofc the 9600gt wont run games in dx11 mode, but that doesnt mean it cant take advantage of whatever dx11 software there may be around... windows 7 for a start... while theres nothing wrong with my answer, theres nothing wrong with the 'best answer' either