Would need to be pretty tight seal on plexi glass or regular glass and tiled around the display but it could be done (and easier on new construction) for sure. I've seen these in show rooms before - the mirror LCD's been most common.
one of my relatives is a contractor. He worked with his electrician to put a 23" LCD into a shower. They had the space to build a small closet behind the wall with the showerhead. They built a few shelves for towels or whatever and also the digital cable box. They used a piece of Plexiglas that spanned the entire wall.
An alternative that I've seen all over the place is to have a 30" plasma hanging on a wall angle arm mount that's on the opposite side of the bathroom (i.e. the dry side), but angled so that it's visible from both the shower and the toilet.