Hi all. Newbie here with a question.The GP in question is actually my son's car and he just got back from college for the summer - point being - I don't work on this car often.
Anyhow, the rear tires are wearing really quickly on the inside edges. I'm sure there is probably some sort of suspension problem (more than one accident!). Can anyone help me out with a likely place to start?

Check your rear trailing arms. (edited, thanks for the correction, Rick!)

Though, you may just need an alignment and some camber bolts to fix the problem.

x2: check for obvious damage. You dont have tie rods on the aft suspension, but you do have lateral arms, trailing arms, strut mounts, spindle bolts, and struts. Most likely, your trailing arms or lateral arms are bent. You may need to get an alignment to see whether it's time to install camber bolts or replace the suspension.

As suspension ages, the car will sit lower and lower, causing odd suspension geometry. I decided to protect my family by replacing all pieces of my suspension with slight upgrades, and the change is BEAUTIFUL. I authored a thread here by the title Suspension Initial Research that covers a vast number of questions and concerns. Toward the end of the thread is a write-up (that I should have spent more time on) that shows the removal and install process, as well as components purchased. The total parts bill came to about 1500 USD.

Welcome to the board, hope we can be of service and that you enjoy your stay here.

1. The rear springs are shot which caused the car to sag wearing the inside of the tires.
2. He drives around with 4 friends in the car and the trunk full of stuff weighing it down, again wearing just the inside edge.
3. It just needs an alignment.
4. Did he lower it? This is common of lowered cars because they can not adjust the camber enough to compersate for the different geometry.

I just installed new MOOG rear springs on my car. My wife drove it and asked what I did, as the car drove much better.

Welcome to the board and ask away. We are here to help and not flame you for asking, unless it is a question that has been beat to death, tehn we will only flame you a little.
Read this FAQ post as it has lots of good info.
http://www.grandprix.net/ubb/ultimatebb.php?ubb=get_topic;f=1;t=004227