Well buddy, it's a 50/50. I've been wanting to put an 04 cluster in my 2000, and have gotten conflicting reports. Some claim that they had 0 problems plugging in a different year cluster, some say that it didn't work. If you buy a whole new cluster, I recommend having a certified shop doing the swap as the chance that the mileage will have to be reprogrammed is high. Due to a wiring difference between the 99-01 and 02-04, if you put an 02-04 cluster in your Jeep, the seatbelt light may stay on all the time, but the other indicator lights seem to work properly.
An 01 is said to work fine after a mileage reprogramming.
There's a lot of information here: http://wjjeeps.com/gauges.htm
Current: Gen 3 Projectors | Light Bar | Hella 500's | Shorty Antenna
Future: LED Interior & Exterior | SRT Reps | '04 FE Conversion