Stalling from Overheating
 

My coolant expansion tank started leaking and my '99 overheated to badly it stalled the car. I was in an unsafe place, so I refilled the antifreeze and limped along fur eight miles, and it stalled from overheating again just I made it home.

Have I ruined the engine? I've read on here that aluminum blocks respond especially poorly to overheating. A search on this forum for provided very little information.

I'm interested to know what you think.

It is common for the heads to crack How hot did it get ? You will need to fix the expansion tank and then see if the system will hold pressure .

You could do a compression test and a vacuum test.
Those two tests " DONE CORRECTLY" will give you a very good baseline on engine condition.

Correct your coolant leakage problem first.

It went all the way up to 250 degrees, the extreme right side of the gauge. :(

After I put in the new expansion tank, I'll do the tests blue62 recommended and see what happens.

Also do as Gabe says.
Pressure test the coolant system, after replacing the coolant tank.
A coolant system pressure test kit can be had from Harbour Freight for around $90.00.
The kit has adapters so you can test most any coolant system out there.
Also allows you to test the coolant cap.

If you need pointers on correct procedure for compression testing and vacuum testing let me know.