I am afraid you are in for some real work, if the resistor is bad.
I have a friend who had the blower motor fail on his 2001 Discovery, which in turn burned out the resistor pack, due to lack of air moving across it.
He tried to remove the lower dash vertical wall to access it, but was unable to do so. He took it to a Fleetwood dealer, who then sent him to a Freightliner shop, who had to partially remove the upper dash, in order to access the pack.
In the process, they cracked the 'nose' piece on the dash, which then had to be replaced. AAARRRGGGHHHH......
If it will help, PM me your Email address, and I will send you the information on the DENSO HVAC system used in your unit. It will give you some troubleshooting information, which should tell you how to check the resistor pack remotely. I seem to remember that resistance measurements from the HVAC control panel will verify a good/bad resistor pack.
If you are a member of the DOAI, the information on the DENSO system is on their Hints & Tips section, and also in their Discovery Forum (Yahoo) site's file section.
2002 Discovery 3126E CAT
2004 Saturn VUE
Mountain Master Tow Brake
All I have ever seen are in the blower box where the heater core is. With the new electronics it could be different. I have an 04 Adven. and that is where it is. My friend has an 04 Bounder and it is the same as mine. It will be a little red flat piece with 3 or 4 wires plugged on it. However do take it out to test and put power on it CharWan