Thanks !
PLATFORM=qt4 builds in scratchbox for maemo5 and it runs on n900, but the window content limits itself to a small portion of the screen (320x480 according to src/constants.cpp I guess).

Changing only WINDOW_WIDTH and WINDOW_HEIGHT (to 480x800 to match the n900 screen for instance) makes the splashscreen and menu behave "properly" (splashscreen labels aren't resized but reorganized to fit screen, and menu buttons are larger - to fill width).
The game board itself is still the same.
Is this expected behavior, and/or is there a better way than changing constants in constants.cpp to fit screen on maemo5 ?
By the way, maemo5 has qt 4.7.4 (< 4.8.3).