How hot does a car have to get till it causes major engine damage my car recently over heated big time the colant was boiling out of the tank and my car let out a blanket of steam

 

Usually you don't want it too be get over 260. I've got it that high a couple times and no damage, but I have a fairly new motor.
How many miles are on yours?

The main thing that gets damaged other than the cooling system itself (WP seals, rad. hoses, thermostat, etc), is the head gasket.
There are two ways I know of to test it. First, wait till it's cool, take it for a drive, romp on it and look for smoke. The second is a compression test. Obviously the latter is a little more scientific and probably more informative. YYMV.

Ben

 

on top of what ben said, prolonged exposure to temps over 260 can warp out the cylinder heads, and it can cause oil to sizzle away inside the engine, not good. this actually has happend to me, in my 69 fury. To answer you question tho; as long as you caught it and pulled over you should be ok, as the engine didnt have to get any hotter. In my case, I didnt have a temp gage and jus put the thing together, and im not sure if i did warp the heads as i havent driven it since that day, the oil light was my warning sign