Do some searches. There's tons of posts about differences between the AP1 ('00 thru '03) and the AP2 ('04 thru present).
Both models are great cars. Biggest difference is the motors. Ap1 was 2.0 liter with a 9k redline. AP2 is a 2.2 liter with an 8k redline, slight torque improvement and slight gear differences. Other minor refinements have been made over the years. Some guys like the latest and greatest (me) and some guys like the higher revving AP1. Drive both if you can.
When shopping, just try to find the lowest mileage car that you can afford, regardless of the year. Stay away from cars that have been "modded" as they have also probably been "beated".
If you find one that looks promising but need some more advice, speak up. There's some very knowledgeable people here that can be very helpful.
Welcome aboard and good luck finding your car. Take your time and get what you want. They're great cars, you're gonna love it!