Zero.

I downloaded ubuntu source package. Build debian package, copied to N900 and yeah, it ran. Ok, no sound because the music files are ogg and N900's SDL does not support ogg. So I compiled an SDL_mixer with ogg support as linker library and got sound.

Next step was to fiddle a little bit with user control (adding accelerometer and proximity support, changing keys to support Game Gripper). Last but not least a few adaptions to debian package structure for better N900 support (icon, menu, optifiy etc) and that's it.

All in all not more then 10 hours work including testing. Of course it is not perfect yet (e.g. would be nice to have touch screen support in main menu or adapt screen size to N900's geometry) but it works good enough to have some fun.

Regards, gilead