I have a 98 as well. Before you buy a new carpet, try pressure washing it. Just be carefull with the nozzle distance, you can separate some of the carpet strings. How do I know this? uh huh. Seriously though, it was easy to do.
Only have to unscrew the center console (not remove). You do have to pull out the back seat if your doing all of it, but the front seats can stay in. Some plastic hold down tabs are up along the firewall, so get a flashlight and find them, they pull right out. If the carpet doesn't pull out, just figure out what it's stuck on. You don't want to just go yanking on it and have a tear.
I used some mildew soap for the pressure washer mix. Gen purpose type for vinyl siding, but heck you could use laundry detergent (no bleach), just need soap. Pull the carpet out, hose em down, soap em down, wait a bit, then pressure wash the buggers. I was very surprised at the outcome. Let them sit overnight outside to drain and dry out. Saved me from buying new carpet that the wife wanted and I didn't. Mine are light gray again
BTW, mine has lived through two kids. It was mostly brown and black in color and I swear some things were breeding in it as well. I thought there was no way it could be salvaged.