On a '97 TJ, you will need to remove the dash (as an assembly) to get to the HVAC housing. The housing will need to be removed to access the evaporator coil. Removing the dash is not too hard on a TJ, I would recommend getting a copy of the '97 factory service manual and following the procedures in it for best results. Remember that the dash was installed basically as a complete unit on the factory assembly line, and that it removes in a similar way.

bill grinder is right, you will need to completely evacuate the system, if you don't have the training and tools, it's best to take it to an A/C shop to have it evacuated and recharged. If the leak has been bad enough to have no pressure in the system for any period of time, or if you leave it open too long, it's best to replace the receiver/drier (or accumulator) when you replace the evaporator coil. More than likely, you will need to add some oil to the system, too. The part number is under the hood on the A/C system warning/spec label.