Once you start ripping stuff apart, you never know what you are going to find. You might discover that you only need to replace a couple feet of subfloor or you might find extensive water damage, mold, rot etc.

I would tear into it regardless. Odds are you just have to replace a chunk of subfloor. Toilets are super easy. Get a new wax ring and maybe a flange while you're at it.

Toilets are super easy.

On one reno I did, the licenced plumber gave up on getting in a w.c. without it leaking. He was used to only working on new apartment buildings. I had to take over and fiddle, fiddle, fiddle.

OTOH, a friend with no experience r&r'd a wc with no problems and was quite proud of his accomplishment. He's a surgeon and has a Phd in aerodynamics. So it's not like he's inexperienced or unskilled in using tools!

Like Bill said, you never know what you're going to find, but this is really not that tough.

You don't say whether you have a second bathroom (or at least a half bath) to use while you are redoing this one. Hopefully you do, and can take your time on this one and do it right and be done with it.

If I understand, right now your layers are vinyl tile, laminate flooring, vapor barrier, tile, underlayment, and then subfloor. Take off everything down to the subfloor and you'll get much better results. Chances are good that the subfloor is the only thing that goes under the tub.
At that point you can assess the damaged area and fix it, then put in some new underlayment and flooring.

There's probably 10 how-to books at your local library on how to do this, with pictures and step-by-step instructions.

Thanks guys! I knew that was the right move, but I was hoping someone would tell me I can take the easy way out :)

Ok, my next concern is: What do I need BEFORE I team into this? I already know I will need plywood which will match the thickness of the existing subfloor (TBD), a wax ring, and a flange. I assume I will need to get some sort of new vapor barrier, because the old one is glued to the ceramic tiles and has fallen apart in spots, although I have no idea what to look for. Then, can vinyl self-stick tiles go right on top of the vapor barrier?

Another possible concern: I've seen in other rooms the subfloor is actually made up of planks, so I can assume that the bathroom will be the same. Does this change anything? Will I run into problems because of the grooves in the subfloor?

I just want to have a list of things I will need to start this because I don't want to run all the way to the store in the middle of this project, and I don't trust anybody I'd talk to in the Big Box Store!

Thanks again.

I think you need to bite the bullet and budget for a new toilet while you're at it. If I'm reading this correctly, your toilet is an ancient water hog that hasn't been replaced in many flooring changes. As a couple of people have pointed out, dealing with toilets seems a lot scarier that it actually is - the old wax ring is fairly disgusting in appearance if not in actual fact, but you'll live through it. There's a thread on the bath forum at the moment about choosing which new toilet that has lots of good fact and opinion on it that might help in making a decision on which one.