350D & 70-200 is Usm lens too heavy or not?

The lens weight is irrelevant to balance with a heavy lens. You hold the lens and your little camera just hangs off the back. The only problem would occur if you tried to hold your camera like a point and shoot with one hand on each side of the camera case.

Wow thanks everyone, I've been absent for a few days. I alway support the 70 -200 lens and mount the lens on the tridop. One day I'll upgrade but till I can be happy with the picture I can take I'll stick with the 350D Thanks again

It shouldn't effect the camera but it could effect your comfort. Sometimes when people get bigger lenses on smaller bodies the stress of trying to support the extra weight can lead to tired or sore hands. It depends on how big your hands are and how you support the camera. As long as you use the tripod collar for mounting when you do use a tripod there shouldn't be any way that lens could harm your camera.