That's pretty hot for anything in your PC to be getting. Even if it's not heat causing the problem, I'd definitely invest in a couple of case fans if I were you.

I doubt you'll notice much of a performance increase in changing to a 7600. I have a 7600GS in one of my computers, and it didn't really provide better performance than my 6600GT which I had in my main PC. That could be something for you to consider.

When I say ADSL, I mean the length of cable from the router to the phone jack. Unless you're actually using cat5 as your phone line (possible, but not standard), it will be a different looking cable.