I looked all over the site and did all kinds of searches for this, but found nothing that actually explains this.

How the hell do I install gstreamer so that I could play mkv files?

p.s. sorry for being a noob

As far as I am aware this is the one format the N900 does not yet support, officially or unofficially.

I would be interested myself in mkv support but as I have all the repositories configured and have not found anything related, I just do not think its available right now.

Also, the thread title does not really make sense. You are not asking how to install GStreamer, its installed out of the box. What you should be asking is how to install GStreamer MKV support. Not everyone will bother to read a thread with a misleading title, I only read it myself because I wondered what on earth you were on about.

oh I didn't know that. I read somewhere to do apt-get install gstreamer0.10-blah blah so I thought it's something I installed as add-on.

Anyway it also says to do:
/usr/bin/tracker-register-mimetype -c Videos -a video/x-matroska

but when I issue that command it says there's no such file tracker-register-mimetype. What is that supposed to do?

Also, I transferred a few videos onto my N900, 5 movies and 1 tv show. All the movies seem to work great, but only the tv show is very laggy and annoying. In its properties the data rate is 980 kbps, and bitrate 1111 kbps. I compared to the other movies' properties and it seems a tiny bit higher. Is that why it's lagging?

I hanen't seen any other codecs in extras, so I'm assuming there are no updates to improve playability?

Looks like gstreamer-plugins supports mkv files "typefindfunctions: video/x-matroska: mkv, mka"

http://tomch.com/wp/?p=116

To install run this in a X-terminal

sudo gainroot
apt-get install gstreamer-tools

"Unable to play media. Video codec not supported."

I've allready instaled gstreamer-tools.
But i'm having a problema because i can install 'i am here' app, because of the gstreamer0.10-plugins-good-extra . I think i dont have it : \
How can i get it?

Please help, thanks.

Install Extra Decoders from your App Manager (make sure you have the Maemo.Org application catalogue enabled).

I've allready instaled on my device.. : |

So the questions are:

What resolution video are in your files? (Should be 800x480 or lower)
If H264, what H264 profile have your files been encoded in? (If not Baseline, then they won't play as the device is not capable)