Yeah thank you guys! The info on 18th page worked for me:
I have uninstalled mypaint in xterminal, installed it back again and installed python-support. App launched from shortcut. Time for testing...
Thanks again!

ps.

Can someone explain to me how the heck does the n900 resistive screen KNOW how much pressure I am applying with the stylus on the screen?
I thought that resistive screen's touch recognition was either 0% or 100%, nothing in-between...

I mean, I own a wacom intuos 3 tablet and I can see that the wacom pen has its own pressure sensitive tip (spring or sth actually measuring the amount of pressure applied, this is happening INSIDE the pen) and the tablet is for checking the position only. Or am I mistaken?

Cheers,
Ralph