If your having a problem playing ISO DVD's or mkv video files in Media Center (vista is the only thing i've used, might work in xp) then try this out:
First, you need to get media player, not media center, to play your mkv.
If you cant get that, then media center wont work anyways.
To get that working, download zoomplayer (google search, standard is free).
Install, and install all missing codecs (it has something called an install center, use it)
Get your mkv playing in zoomplayer and it will probably work in media player.
if not, search google until you get that working.
I've added folders to watch in media center, but it never finds the mkv vidoes.
To make media center find these videos, so you can play them from the interface, add a shortcut to your "My videos" folder
to the HD movies. you might not be able to get a Tree folder to work, you might have you link each folder to my videos.
They will then show up in media center and play with no problem.
To get ISO DVD to play.
As you might have 100's of DVD in iso form, you will want these to play in media center.
First, you will need to extract your ISO to a folder, it will create video_ts and audio_ts folders. dont touch them. make sure they are in a folder for it self.
You can then delete you ISO as they burn the same.
second, go here
http://support.microsoft.com/kb/930526Follow those directions.
Restart media center (maybe twice)
You will have a dvd libray folder now in tv
Add a shortcut in your "my videos" folder to the DVD folder (where the TS_video and TS_Audio is located.)
you then need to ADD the DVD folder form this screen in dvd library.
this is a different libray from the other one.
Add "My videos" as a folder to watch in the DVD library screen.
your done, your ISO's will show up here now