Acoustic Dampening?

[G9logitech]

Hey Guys -

I just got done building myself a HT room to watch blu rays in; as well as listening to music in.

Question is: Is there something I should place on the walls, such as acoustic sound dampening so the music/sound doesnt bounce around? Since I built this room somewhat small, and the walls are hollow with only cheap wood peices that come pre fabricated to fit into grooves of one another.

Something thats not overwhelming huge, like someone saying, what the heck is on your walls (like those big pyramid cones or what not)

Thanks guys