Get yourself a used PS3 to use as your media server. Prolly get one at a pawn shop or 2nd hand somewhere for a fraction of the retail price of a new one. Since you only want to use it as a media server it doesn't matter if the CD drive in the PS3 works or not. I'm using a PS3 with a broken cd drive as a media server and it works great cause the kids can't put any games into it.
I used a program called "PS3 Media Server" for the longest time to watch movies and TV I downloaded until I got a Netgear R6300 router that has a media server built in but still use the PS3 as the renderer. PS3 Media Server
Watching movies on our 52" plasma is awesome and heck of alot better than before when we watched on the computer monitor.
Also I found out that wireless isn't all that great for streaming video so I've hardwired my PS3 in and have had no problems with streaming video at all. Your not using any internet either while streaming since your within a home network all your using is the ethernet cable from router to PS3 console.