well it'd really help if you posted a budget for the system and if you'll be needing an OS, keyboard, mouse and monitor. (the monitor/keyboard/mouse should probably gaming hardware if you're gonna build and gaming rig) I'd also help if we knew whether or not you're going to overclock the parts (that's really why Core 2 Duo's are so great. If you overclock them you can get them almost twice as fast as stock.)
I'd drop the E6700 and get an E6600 and upgrade the mobo to a Gigabyte DS3 if i were you. You should really get a better motherboard for that nice of a processor.
The PSU: I really don't know that much about the neopower models but i'm very satisfied with my Truepower II. 550W is enough for that system but you might want to get something more powerful for the future like a Truepower 3 650W or a Thermaltake "Toughpower" (i think that's the name) 650W. With more power-hungry graphics cards coming out upgrading might be hard later on with a 550W PSU.
Memory: if you're not planning to overclock then this memory should be fine. if you decide to overclock then i'd suggest the G.Skill DDR2-800 2Gb (2x1Gb) kit. (there are 2 of them to my knowledge but the value kit will still oc pretty well and is about $100 cheaper.)
Graphics Car: It's really a tough call for this right now with the new Nvidia and ATI cards coming out in a few months. The 8800 is out now and apparently amazing but i have yet to see it. It's around $500-700 depending on which model you get (GTS or GTX). Really what i'm saying is that the 7950GT you've got there is good but you'll probably want to upgrade it in about 1-2 years to keep up with new games coming out.
So you've got 3 main choices:
1. Just get the 7950GT and have great graphics for a year or two before upgrading
2. Get a really good card for around $400+ and not upgrade for like 2-4 years
3. Get a decent card Radeon 7600GT or ATI x1600 for example. and then wait for new cards to come out and prices to go down after 1/2 a year and then splooge on those.
*the above are just estimates as to how long the cards will last you. it really depends on if you want all the graphic settings on high and what not for how long it'll last*
i hope that helps you out some. i'll be able to be more helpful if i know a budget and all that information.
Antec NeoPower 650W
Intel Core 2 Duo E8400 (w/ Arctic Freezer 7)
4GB DDR2-1000 G.Skill
Sapphire x1950 Pro 512mb (w/ V700)
250GB, 500GB and 1.5TB Seagate Barracudas (2.25TB total)
Fatal1ty XtremeGamer sound card *** generic TV tuner
Xclio 3060 case *** HannsG 22" monitor
XP Pro / Ubuntu 7.10 *** Razer Copperhead and Tarantula