2002 ram diesel 2500 4x4 Heater Core

I have some occassional steaming of my windshield and slight coolant smell in the cab...suspect heater core is bad. Removed glove box door and looked around and can see some green residue in the area. Not much water leakage in the cab. Very intermittant. I can see the inlet hoses for the core and the box it resides in. Is it really that big of a job to replace? Looks like I can do it right thru the glovebox. Could this be a clogged drain line and not the heater core? I drive a lot; been having bad headaches -wondering if this might be the cause. Any useful input would be appreciated; never found a job I couldn't do but I've read some horror stories regarding heater core replacement. Does the A/C come into play?

I haven't done one yet but here's a pretty good video,

http://www.youtube.com/watch?v=dTlZwJqgR3o

Thanks, that video is pretty good. The 3/4 ton cab may be a little bigger and have more room side to side... I may be wrong but I think I can get this thing out without dropping the steering column. That video doesn't mention emptying the A/C and recovering the refigerant. That would be the kicker for me. I'm still not convinced that the core is bad, I get some smell and steaming every now and then but can't make it do it when I want to, but I am losing coolant slowly but steadily somewhere. Man, after 230,000 miles these things just start falling apart.

Did this on a 96. Steering column, 2 bolts. Left A/C system intact.