Couldn't sy why, but now I CAN use higher resolutions. Problem is, I can't use higher refresh rates than 74Hz in 1400x1050.
I checked if the card might be the problem but it's listed to support 85Hz at 1600x1200, so it should reach at least 100Hz at 1400x1050 - and that worked without 3d acceleration.
Now I can't seem to switch to a higher refresh rate. The monitor can do 140kHz line frequency (and the SaX2 options are set accordingly) but it doesn't. If I try setting a minimal refresh rate (like 70Hz) I automatically get the lowres problem described above... this strategy did work for my previous card.
Thanks again, and tell me if you need more (or different) info,