I've changed the plugs and wires in my 2000 Montana before. Its a rough job, but doable. I think the only tool I had to go out and buy was a set of ratchet straps to pull the engine forward with. The hardest part of the job, for me, was getting the plug wires off the back three plugs. All three were stuck on tight and I wound up having to split the boots with a pocket knife while draped over the motor and cussing at GM.
There are quite a few things to take apart before you can actually get to the point of rolling the engine forward and getting at the back three plugs. If you can, you may want to note how everything came apart so it can go back together the same way.
EDIT: I'd recommend using AC Delco plugs. I've read that other brands don't last too long in GMs and this is a job you're probably not going to want to do more than once.