What would you say is a good gaming card then? Or what should I look for when buying one?
A) Was already answered by timil. You can disable it though. Why would you want to remove it?
B) The HD7750 can work with a RELIABLE 300w. I doubt the PSU you have is reliable enough for that.
A good graphics card depends very much on the resolution of your display and the games you play, the minimum I would suggest for ANY resolution and game is the HD7770. BUt if you have an HD 1080p monitor, I would say the HD7850/GTX660 is the minimum.
What games do you play and what is your display resolution?