Maximum PC

So me and my roomates decided to put our large tv in the living room. However we were wondering what would be needed to be able to play movies and music ect on that TV from our computers in our rooms? Any suggestions?

Very likely that you already have the tools (equipment) needed on-hand.

Any of those PCs running Vista and/or Win7?
What (if any) gaming systems (Xbox 360, PS3, ??) do you have?

Got a 360, and PCs running Vista or 7? The 360 can natively connect to a shared WMP library on a Vista or Win7 machine (also to an XP machine running WMP10 or 11, and with the Windows Media Connect app installed), and can play most file types (it's documented on the Xbox site.)
IIRC, a PS3 can do the same, as it's a DLNA-compliant media player.

We have a 360 and 4 pcs. How do I go about starting this?

Start here:
http://windows.microsoft.com/en-US/wind ... or-devices