I suggest an Asus P5Q and a Core 2 Duo for keeping this computer within budget, and some DDR2 RAM. If you raised the budget, you might be able to get an i5 in there.
Instead of that GTS 250, pick up a 4870 (Powercolor) for about the same price, it is much more powerful.
If you only need 160GB, then this: http://www.newegg.co...N82E16822136075
This PSU has the same power (on the +12V rail... what really matters) and is modular for less money... also look at the Corsair PSUs, as they offer the best reliability: http://www.newegg.co...N82E16817341016
The case you picked out is fine... you can also go with this: http://www.newegg.co...N82E16811129066
Or just a plain Antec 300 or 200.
This is also a nice case for the money: http://www.newegg.co...N82E16811119137