Is there any possibility on linux to start some parts of kde during system startup? It would cut the time form login to fully working desktop.

afaik there is precious little "dead time" during the booting process, i.e. when you load those libraries doesn't really matter - they still take the same time to load.

One thing you may consider, however, is to login into KDE automatically yet have the session protected with a locked screen. This would take the sting out of waiting for KDM to come up, logging in and having to wait again for KDE to start.

HTH