Had typed in a reply and it got lost...bummer.
Don't use the greenboard, it's basically junk and is no longer in the national codes (maybe not adopted by local yet) for much of anything...there are much better and reliable products. Tearing out the old mudbed walls (floated walls) is messy, the metal lath in it is sharp, and the stuff is heavy. It does make a nice wall to tile on, though. You'll probably find on an old house that the studs are not very even, and are HARD. You may need to predrill.
You need a moisture barrier on the studs (plastic sheeting or roofing felt) lapped over the tiling flange of the tub, then cbu (cement board) if you want it to last. Use real thinset, not the stuff in a bucket - it's cheaper and will last. The mastic (even though sometimes the bucket says thinset, it's not) never cures like the cement, and will soften and can even wash away if it constantly gets wet.
Check out www.johnbridge.com for help with tiling...they'll take good care of you.