Yeah it's possible. I was just hoping to find a way that doesn't involve replacing the stuff mentioned on the post below. You can get away with not having to replace the entire blower unit like the guy did below - you just need to replace the resistors with a power transistor from 99-00 blower unit and you also need a 12V relay for the highest fan setting to work properly.
The heater unit seems to be another matter, as the new one has a servo motor controlling the air mix. The 96-98 heater unit and 99-00 heater boxes seem to be *very* similar. But the new one has the servo motor, and screw holes on the box itself to mount the motor. Also it looks like the newer boxes have newer wiring, which is required to connect up with the new climate control panel. So the best thing here is probably to do what the forum post below says to do, which is just upgrade the entire box.
The post below goes into details on how to do the swap. I can post details myself of how I did things when I finish the swap if anyone wants to know. I have everything I need to do the swap, except for a 99-00 heater box & associated wiring harnesses. I also need the 12V relay on the bottom of the blower. If anyone has anything let me know....
How to do the swap
It's obviously a pain to do the swap. But I think the results are worth it. You can put in a screen where the head unit normally goes and it will look completely OEM - no tacky motorized screens coming out blocking the air vents, nothing mounted on an arm someplace, etc. My plan is to not use a head unit at all and run the audio output of the computer direct to an amp. Then hook up radio to the computer. This means I won't need a head unit cluttering things up. Just a simple screen.
Then, in the place in front of the shifter where the tape deck or CD player normally goes, I'm going to put in a panel with USB/firewire ports, flash card reader, slot-loaded DVD, audio input, maybe a volume control knob or something like that or one of those computer-controlled LCD displays, and perhaps a regular wall-sized AC plug coming from my inverter so the front passenger could plug in his laptop or other item without hassling with an inverter or DC-DC converter. In the end, it's all my stuff and my design, so I don't have to work around any crap from a head unit.