Attention! I answer me myself!

Ok, i have installed it! From the Khertan's site i have downloaded pygtkeditor-2.1.0.all.deb - then i have dobleclicked it - and the application manager says to me, it were something others needed - but this "something" is described true and is on the Khertan's site to find too.
Also, i try first download and then install the needed file - python-pygtksourceview-2.0.0.armel.deb, then after it the pygtkeditor-2.1.0.all.deb. No error message, no prob's, all ok, the editor application is to find under menue in Extras and work very good. (I have made only simply changes on navit.xml, but the syntax highlighting, and other features of the editor looks very good.)

Please, important - not automaticaly installed, not from Maemo site, but downloaded directly from Khertan's site and with simply "windows " doubleclick installed on the N800.

Best thanks to autor and the other peaople, they have been working on this soft.
Feri