You do not need to hire a pro a mount a little 27" sceen, it would probably cost about what you paid of the tv.
Just make sure the screws are in the stud and your fine.
Also sounds like your a renter, get in writting that it is OK to wall mount the tv, if they will not give you it in writting then do not do it.
I want to mount a new, 27 inch flat-screen plasma TV to the wall. What type of "damage" would this do to the wall? I plan on having it professionally installed, but I need to convince my landlord....

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic