Try hooking your PC up to your TV when running at 640x480 and 800x600.
Then, hook it up to a standard PC monitor and see
Try to get a TV about the same size as your PC monitor
If you like what you see on the TV, then composite will be OK for you. If not, then get yourself VGA
That is the best, and most honest way for me to tell you whether you need VGA or not