Won't play Matroska (.mkv) files at all

[jimpeel]

When I open the .mkv files with VLC the window just sits there. The radio buttons appear as though something is there (pause / stop) but there is no control over the file and no sound or picture. The counter reads 0:00:00 / 0:00:00 yet the file is 1.127gB.

I am using Windows XP sp3 with VLC 0.8.6i

The help page at http://www.videolan.org/doc/faq/en/index.html#id238663 states:

1.12. My file doesn't seem to work!

Are you sure VLC supports the file? (It does) Try checking the features page. (I did) If it supported and you compiled VLC yourself, (I didn't) check if you have downloaded and installed all the codecs correctly.

What codecs, where are they, and do I even need them?

Any help would be appreciated.

[VLC_help]

You don't need to install anything. VLC has everything build in. You can try nightly builds, to see if they work better. If not, use tool called Mediainfo to check that the file is valid.
http://nightlies.videolan.org/