Man, my dual 1800's top out at 95F when oc'ed and running folding/seti... Course, I watercool them.
For most AMD systems, anything under 50C (122F) shouldn't be a problem, actually pretty likely they'll be fine even a bit hotter. But 50C is where I draw the line and like to get better cooling happening.
As a general rule of thumb, if you're having lockups/crashes frequently, but the problems don't happen when you cool the system off a lot... you should consider more cooling.
If you remove the side of your case, and notice problems go away... you most likely need better case ventilation (intake and exhaust fans).
If you still have problems w/ case side off... try blowing a full sized floor fan into the open case... if that solves your problems, probably want to upgrade CPU and/or Case cooling.