Pontiac Repair: 1996 Grand Prix blown engine?, engine swaps, blown engine

Question
My daughter was driving her 3.1L v6 1996 GP with 115,000 miles, and the engine just quit. When she tried to restart it, it wouldn't turn over. She had it towed to my house and we tried to start it, it did start, but ran REALLY rough for about 20 seconds then quit, and now won't crank again. I don't know much about these cars, so I'm hoping someone can help me diagnose this, are there any problems peculiar to these engines that I could check? There's no water in the oil, oil is full and clean, she said it didn't overheat and gave no warning except for a slight "hiccup" a few miles earlier, then ran fine as usual till it suddenly stopped. If necessary, how hard is it to change engines in one of these? I've done my share of engine swaps, but not on this newer stuff, and never a front wheel drive. Does the motor come out the top, or do I really have to drop the subframe as one guy told her? Thanks for any help you can offer.

Answer
well drain the water out of it and start it up and see if it runs fine, if so before you go out and rerplace the motor, fill it back up with water and go buy a coolant pressure tester, test it and see if it is a headgasket, and or a intake  thses motors are bad for both , and it will be cheaper than amotor   but first drain all the coolant and start it and see if it clears out and runs good for 30 secsnds or so or leave the cap off and put water in it while its running and see if it starts to miss then pull each plug wire to see what cyl it is