In general, what things need to be repaired on a car?

As a car gets older what are some common things that need to be replaced?

Also as the engine gets older, can you help keep it going by replacing specific parts, or once they start to go is there nothing you can do?

This varies from car to car - some parts will last a lifetime on one car, and on another car, the same part will be replaced over and over again (for example an alternator). However, changing your fluids and filters is probably the most important thing to your engine's health - and what keeps it running the longest.

Im assuming that you have an older car and want to keep it running, so here's a list of work that should be done (if not done already):
- Change oil on a regular basis, every 3000 miles max. unless it's synthetic (5000 miles then)
- Replace coolant
- Replace transmission fluid (and trans. filter if your car has one)
- Replace all acessory belts
- Replace timing belt (check w/ mantineance schedule to see how often)
- Replace spark plugs & wires
- Replace air filter
- Replace fuel filter(s)

Well I dont actually have a car, but im looking at a 98 Pontiac Firebird with 72,000 miles. Im guessing by the time im sick of it, I will have put ~50-60k miles on it... And im wondering it will still be running by then.

People on the Firebird forum dont seem to know if the V6 is reliable or not (although they say the eairly V8 "is a nightmare") so im assuming it's reliability is average.

there is no simple mileage table you can use for when stuff will break or fail. It sure would be nice if everything was that predictable.

Beyond regular preventative maintenance (fluids, ignition components, brakes, rubber components etc), stuff breaks, and it can be just about anything on the car. I could write up a huge "common items" list, but that will do little for you since many common items are so random. For example, a fuel pump is a common failure on high mileage cars, but I've seen them last as little as 30K miles, and as long as 300K miles. So its not something worth worrying about until it fails.