If I'm not mistaken, VGA should already able to support up to 2560x1600, but has a bit doubt about the capability to playback movie through it or games, you can try. DVI or HDMI (they're the same except HDMI can carry audio signals) is no doubt able to transmit full 2560x1600 without any issue.
And since it has 2x DVI and one HDMI, you can use either one. FYI that those tons of connectors is enable support of multiple inputs either multiple devices/platforms, so using one to each device/platform is enough.
42" is huge IMO, not suitable for computer desk, unless you're planning on at least 7 feet away, or you have many people to watch/play in a living room.
> 24" desktop monitor will need quite wide desk or having a slide keyboard to extend the distant otherwise you might strain your eye balls.

Sitting infront of a huge LCD might make you nausea, I remember my sister used to play maple story in front of my htpc, she can barely walk after