okay some more infos...
as i said the sdl module didnt compile yet... wich means i didnt have any working version yet
actually, even my SDL lib is broken (im using ADS 1.2 and actual SDL port for the GP32 was targetted for GCC)
for the scaling issue... i was thnking of an on-the-fly scale down for each frames, but it surely going to slow down.
so if any of you could look at the openttd gfx resource files, and see if it is possible to extract the sprites with some tools, we could the scale down the sprites before loading them in openttd
maybe i'm going to contact the openttd programmers, but i first need to fix my sdl lib