Wayhey! Ikea!
I fixed a piece of wood underneath it to stop it dropping down, then used something on the top to "hold it to the wall"
If its a cavity wall, you can get some proper fixings from b&q or the like, and they are solid (used some to hold my sons dvd and tv to his bedroom wall.
If its a solid wall, just use some normal rawl plugs, 1½ - 2in screws and you should be laughing.
Just make sure there is no electrics behind it