Re: Installing drywall
you can go dirctly over the old plaster but youll have to remove all the trim on that wall then reinstall it afterwords. keep in mind though if their are any windows or doors the jambs will need to be furred out so that the casing will meet up with the jambs.
if you remove the plaster and lathe, youll be into a different situation, the old studs will need to be furred to make the wall flat. typically with old homes with plaster and lathe, if you hang the drywall direct to the studs the wall is going to be really wavy
fire up the saw and make some dust