I did this job about a month ago. The link up there by lazyxj is very good and helped out alot...I used it more than the FSM. You do not have to remove the steering wheel, just lower the column. The fit is a bit tight to get the dash over the steering wheel but its doable. I did the job by myself and it took me just about a full Saturday from about 9 in the morning until 7 pm. One place where a helper can be useful is putting the climate control box (housing that holds the evap and heater core with all the flaps and stuff) back in...someone to help line up the studs with the holes through the firewall and to get the nuts threaded back on from the engine side. Have a bench ready to put the climate control box on when you get it out to open it up and replace the evap coil/heater core as you do not want to mess this up and reinstall everything only to have to take it apart again. Make sure you have the tools for the quick disconnect fittings on the evap lines. I also replaced the heater core, and the receiver/dryer while at it (receiver/dryer is cheap, and w/150k+ miles I don't want to have to go back in there oneday for a leaky heater core). Also make sure you follow directions to disarm the airbags before starting. Ziploc bags with a marker to label all parts/screws (takes more time up front but saves time in reassembly). Also make sure you get the climate control box reassembled correctly (blend doors, vacuum lines hooked up). I just drove it to a shop when I was done and had them pull the vacuum on the system then charge it and add the PAG oil (the FSM tells you how many ounces to add based on the components replace). I'd rate myself as a medium-skilled mechanic and it wasn't hard or technically daunting, just a lot of work. Definitely remove at least the front passenger seat will make the job easier too.
Details details on reassembly (wire connectors reseated right, vacuum lines in right place). Also, just to be on the safe side, I also ordered an o-ring kit and replaced the o-rings on the evap coil pipes and receiver/dryer (re-used the low-pressure switch).
Edit: Add one more thing, have replacement heater core hoses ready! I could not get them off of the old heater core and had to cut the hoses.
One more edit: '98XJ Classic w/4.0