It's actually not that old, you have plenty of options! If you are fine with doing the wiring yourself all you should need is the following:
1) A radio (commonly called a "head unit"). Simple one's that play cd's, fm, and have USB and/or AUX inputs can be had for about 60 - 75 bucks now a days. If you can, try to stick to name brands like kenwood, pioneer, dual and JVC. You can go online to crutchfield.com and they have a tool that will tell you what you can use.
2) A wiring harness. This will plug into your stock wiring harness and then all you have to do is line up and solder the wires off of it to the wiring harness that comes with the radio.
3) A dash kit. This will hold your new radio in place and make everything flush. It's also needed to utilize the screw holes from where the stock radio sat (I believe).
I have yet to actually change out the radio on my expy since I've got the MACH audio. I've heard that that's a whole different can of worms. I'm assuming since you have an XLT it probably won't have that. As far as installation goes, you can pull the dash apart yourself and go from there. I believe the facia around the radio is simply held on by clips. Alternatively you can just go to best buy and spend probably around 200 and that will include the new radio and the install.
Also, if you order online through crutchfield they will send you the wiring harness and dash kit for free (I believe) and give you vehicle specific instructions on how to do the install. I've heard they have really good tech support as well if you get stuck.
I just installed a dvd unit in my wife's grand prix last weekend. Took about 2 hours.