go to this link, order plaster washers, they come with instructions. make very easy excellent repairs for cracks and crumbly parts you worries about
plaster is much better than drywall and should be restored when ever possible. the plaster washers make the repair arears stable and sound
BTW, there is alot of frameing work to be done on plaster framed walls to prepare for drywall, its not just a matter of swapping the coverings
its not extreemly difficult my it aint the easyest thing in the world either
much easyer to just repair and you end up with desirable plaster and not modern cheapo drywall
what i would not give for plaster walls in my house!