Re: What NVidia-Card for Linux
It sounds like the X3100 will be sufficient for your needs. A friend of mine has a GMA 900-powered laptop and even it runs that resolution with compiz incredibly smoothly. I can imagine that the X3100 would have no problems whatsoever. In this case, closed source drivers are not an issue and Intel has been proactively developing their drivers for a few years now. Historically, Intel has the first graphics vendor to implement features like texture_from_pixmap and xrandr 1.2 (indeed, Intel's own Keith Packard architected xrandr 1.2).
The X3100 has native support for HDMI although I'm not sure how many motherboard manufacturers are presently exposing this capability. Sorry I can't recommend a specific mainboard, it's been a while since I built my last desktop. I hope this helps.