I have a 1920x1080 flat panel plugged into a DVI port (with a DVI-to-VGA adapter that came with the computer). I assume that this cabling kludge is what's preventing Mint from correctly identifying my monitor and offering to set the correct resolution. In any case, I'm able to use xrandr to get the correct resolution, and I've added the commands to .Xsession to make them permanent (following instructions found elsewhere on this forum).
The problem is that, although kdm comes up in 1920x1080 mode, it doesn't seem to know it. The logon screen displays in 4 quadrants, with the input widgets and menu in the upper left quadrant, and the wallpaper tiled in the rest. Is there a better place to put the xrandr commands to prevent this? Or can I set some kdm configuration so that it 'knows' its in 1920x1080 mode and formats the screen correctly?