Optimal speaker placement is mainly a result of experimenting with different positions. So putting them "right up against the wall" (front wall I presume) may or may not be the best position. Usually, you would want at least some distance from the wall (it could be a matter of only a few inches). However, putting them right up against the side walls is definitly not a good idea.
Even if you absoulely have to put them up against the front wall, it will be a heck of a lot better than in the wall.
Don't know if the VP150 can be wall mounted or not but mounting speakers on a wall especially a center channel speaker can be an iffy proposition but you won't know until you try. It may sound just fine. I've heard wall mounted centers that did sound very good.
Mounting surround speakers on wall is not too bad because the surround material usually doesn't contain dialogue and other such critical info.
