Well, you didn't really give is much to go off of.
We need a power supply, country, budget and other things like the specs of your computer and the games you are trying to play.
And manofchalk, they don't sell that 9800GT any more. They do sell this one:http://www.newegg.com/Product/Product.aspx?Item=N82E16814130534
Also, DDR2 is only for the computer. The GPU has its own modules.