the 775 is a good socket, but id suggest going for the I7 920
you should not use your old DDR chips, it will not work.
4GB DDR3 is plenty.
for the GPU, that is a good card, it really is, but if you want equal performance, maybe a bit more, and DX 11 *newest* get the HD5770
it it IS EXTREAMLY good to get the 4870 or the 5770, it will be like night and day compared to your old GPU
like VW bug vs. a rocket ship kinda difference.
You could keep your same power supply, but id suggest to get a new one for this biuld, it IS the most important part of a new build, and you dont want to destroy your nice new parts with an old used PSU
And agian, id suggest getting a new HDD, you can get a 640GB one for about 60 bucks. Due to HDDs failing after a few years of use, its always good to use a new one in new biulds.
though id say it is ok to reuse the disc drives.
they arnt used as much as HDD so they usually last longer.
both cases look good, though i an personally say the 1200 kicks some serious ass. I own one myself.
with the I7, that ram you picked, either video card i mentioned, and a new HDD, id say that you would have a pretty good gaming machine there, you could easily play Crysis.
I have my own youtube channel, and i post recorded videos about some PC games, and upload them to show others, kinda like a video demo of selected games. In my PC i use a HD 4850, and the two cards mentioned, are about 25-45% faster then what i use. And with that set up above, you could play games maxed for sure. If you would like, here is my
for examples of some games you could easily play.