Thats difficult to understand, sorry.
My problem is i cant install application like "i am here": http://talk.maemo.org/showthread.php?t=50246&page=27, because that file i've mentioned.

my old p990i can play mkv movie but this n900 can't even open

Not true: about half of the videos I've got on my N900 right now are in MKV files.

A few items to note:

1) The MKV, or Matroska, file format is not itself a type of video - it is a container format, which can contain videos of many types. All the video players I've tried so far on the N900 can handle the MKV file format.

2) The N900 is quite capable of playing a decent range of video codecs. If the video you are trying to play is not supported, however, you can fairly easily convert it to a supported codec. The Maemo.org site has a good wiki page on how to do this:

http://wiki.maemo.org/Video_encoding

i think the main problem is that resolution of videos to be played by N900 is limited by design to display resolution.
most mkv will have higher resolution.

There are a number of factors that can cause a video to be unplayable on the N900 (or any other cell phone) -- the display resolution, the compression factor (or bitrate), the codec, the file format, etc.

But all of these can be amended by re-encoding the video into a form the cell phone can use. A video is, ultimately, just data; converting that data from one format to another is easy.