Go to
www.kbb.com for pricing and all the goods on a new X (or any new rig). I have no idea what Nissan is charging for a '02 SC, but KBB will give you an idea of what the dealership paid for it.
The only thing the site doesn't tell you is what kind of kickbacks Nissan is offering dealerships as sales incentives. With the market the way it is, you should be able to get a new Xterra for a great price (i.e. much less than MSRP). However, if you're going to trade in a vehicle, be prepared to get screwed. Dealerships are low-balling trade-ins to make their money.