Jake,
Overall, your system looks good.
I would choose the GIGABYTE GA-965P-DS3, based on several reviews it gives very good performance and is at a good price point.
As for the GPU, since you are not going to be gaming much, I would stick with the 7900GS you selected or drop down to a 7600GT, or perhaps a 7600GS. You don't need to buy a X1950Pro like others are suggesting since it's most likely an overkill.
Regarding the power supply, I would go with the Corsair 520w PSU since it is a derivative of a Seasonic S12 PSU. I have a Seasonic S12 500 PSU and I can say it is a very quiet PSU. The Fortron 450w PSU is both good and inexpensive and will be more than enough to power your proposed system.
Keep the Dell 20" you have listed. It uses an 8-bit LCD, which is far better than a 6-bit LCD screen used in cheaper LCD monitors because it provides better color accuracy and crisper text. The down side to 8-bit LCD screens is price and the response times are not as good as 6-bit LCDs.
Lastly, instead of selecting the E6600 you could opt for the C2D E4300 CPU which has a clock multiplier pof 9 (just like the E6600), but it only has 2MB of cache and the default FSB is 800MHz instead of 1066MHz. It also lacks virtualization. The average performance difference between 2MB and 4MB of cache is about 3%-4% in most applications; including games. The one exception is multimedia encoding where the performance difference is 10%. The
C2D E4300 is currently selling for $179 compared to $316 for the
C2D E6600.
There have been several reviews where the E4300 has been push as high as 3.2GHz - 3.4GHz. I'm not pushing you to go with this CPU, I just wanted to put it on the table as an alternative.