Graphic resolution in guest OS

[Apteryx]

Hi to all,

I've searched for this in the forum but I didn't found any answer (useful to me anyhow).

I'm experiencing a problem with the resolution on my windows XP guest OS under VB 4.1.22, I can't switch to any true color mode, even if i can run windows in 1900x1200 (a very high resolution) but always in thousand colors. Some applications (graphic and games) need a true color video card, so they fail to load.

I've installed the guest additions and the 3D support. I've tried to check-on and off the 3D acceleration in the options menu, but nothing seems to work.
Under the advanced options in the video card drivers, I can see all the true colors resolutions available, I can select and run all of them, but at the end the display remains Kcolours.

Any idea/resolution for this problem?

Thanks a lot
Alex