Hi again Andy,
I've familiarised myself with modelines and tried various things: 800x600, 1024x768 with various frequencies, etc. Nothing works yet. With 1024x768, always get patterns that look the same whatever vrefresh I try. Different patterns for 800x600. Don't know what's going on... thought it could be some fundamental problem or a BIOS setting but the fact is that the same XF86Config file works with the XFree nv driver...