Flight Simulator X for instance is very CPU dependant. The majority of games however require a good CPU, but the GPU is more crucial for High Res gaming. I would choose the lower CPU with the better GPU since you did state that it's High Res gaming you are planing to do. Also it should be noted that with the right Motherboard that E4300 can be overclocked, so you can get bring it up to E6600 speeds or exceed it.
Definately get the e4300 or 4400, which can be easily overclocked to 3Ghz or higher, especially with that board. The only diff between a 2.4Ghz e4300 and a 6600 is the 2mb of cache. As for the card, go for the 640 MB if it is truly high-res. What resolution are you thinking of?
Either way, your real bottleneck to gaming at all with those parts is the 1 GB of RAM. Go for 2 GB, period. The switch from one to two gigs of RAM for me was the difference between BF2 at medium-high settings to BF2 with 4xAA, 16xAF, and everything else cranked all the way up. It was like night and day, and on my 7600 GT I still get 60+ frames!
cpu-intel core2duo e4300 or e6600
ram-a-data 1gb 6400
vga-asus 8800gts 320mb or 640mb
So my question is what will be better for me e6600 with 8800gts 320mb
or the e4300 with 8800gts 640mb, and this system is for high-res gaming.
If i were you i'd choose the following:
NVidia 8800GTS 320MB
The E4300 is a cheap and highly OC cpu.
I think more RAM it's really important for overall system, for latest games and OS.
320MB is more than enough for next games except if you play in very very high resolutions. (What monitor/display do you have? What resolutions do you usually play?)