Thank you

This is awesome, WMP12 couldn't stream files from an external HD, PMS didn't work at all, and I wasn't about to pay other programs and risk them doing nothing.

Now I'm able to stream all my videos to my PS3, and it doesn't matter if they're on my main drive or an external HD, what their file-type is, or how high the resolution is. Thanks.

Seconded!
I bought a Panasonic Viera 50-inch plasma yesterday, and read that I was supposed to use TwonkyMedia as my DLNA server. I then did some research and came up with Serviio and Mezzmo, with much opinion favouring Mezzmo.
So I downloaded the trial and installed it.
I tried MKV, MPG, MP4, AVI and VOB. While one or two worked well (with specific reference to fast forward and play functionality) most simply stopped playing and returned to the folder view.
I then uninstalled Mezmo and tried Serviio.
What a difference! Every video file I have tried has worked perfectly. The folder views are accurate, and I am amazed by the classifications that have taken place, e.g. by actor, by genre, etc. One curiosity which I cannot explain: I have a genre called Erotic, in which many very similar-sounding titles (e.g. I Tvillingernes tegn) are listed. I have never heard of any of these, though they are all recognizable as something else. For example, documentaries on Indira Gandhi and a Christopher Isherwood are included here.

I have only the highest praise for this product - and the fact that it is free is extraordinary.