well the best thing u can start doing is useing google.com and researching stuff. Thats where you well fine out what parts you well want is by reading reviews i am sure we can all build a computer for u and you would like it but you wouldn't know what was the reason we picked this or that part and then if something happens you woudln't know what to fix or what was wrong with it. I would read reviews and they gave u soem good guides to look. Just take your time don't rush into anythign at all it isn't smart.
Also you could get the 6800GT or you could get SLI or you could even get the 7800 and run all the games you want but that is where reviews come in handy