Stream movie from PC to TV.

I have a computer at the house i collect of digital movie . In another room I have a TV. I want to stream a selection of MKV and AVI videos to the TV. I can also put the movies on an external hard drive  if that makes it easier for me. What would be the cheapest way to display the movies on my TV?  Solve this problem would make me finally watch a nice movie in my house with my kid we do like it specially there's a bunce of good movies today. 

I Get into the habit of moving my  other media files off  to my PC either an external USB drive or a Home Server.
 but seems to be more reliable on PS3 and install it on the computer with the media. there are many options on this. browse content and hit play. So note that if the file has encoding errors on my PC may just work but i keep playing where the PS3 or X360 a simply way  to play the file. The device is including Xbox connected to the TV to find  stream  content to the TV. If you have both an xbox 360 and ps3 on network connecting 2 different tvs to computer holding all vids. this is extremely easy to use for streaming pics audio and video and the 360 is a also good.
this is compatible from XP using media player 11 and from tiger using PS3 extender.