Xfbdev and frame buffer resolutions

Hi,

How can I change the resolutions that Xfbdev use ?
It always starts in 1024x768-70 no matter what resolution I 
have in console (I set all consoles to desired resolution 
with fbset -a 800x600-75 for example).

If I use -screen option it looks bad like it tries to render 
1024x768 pixels in a 800x600 space.

Should I tinker with kmode.c ? I am using viafb as 
framebuffer driver.

Thanks,
Nicu.