Whenever I install Mint on my main PC one of the more annoying problems is the resolution of the screen at login, after installing the latest ATI drivers it is always set way beyond the ability of my monitor to display (native is 1440x900, actual resolution 1600x1200).
After much searching and a little bit of digging in the help files I have come up with this solution.
> sudo dpkg-reconfigure xserver-xorg [Follow this through to the end]
> sudo aticonfig --initial
> sudo aticonfig --resolution=screen#, WxH [Where screen# is the display, if you only have one this would be '0'. and WxH is your desired resolution]
Hopefully this will help someone else, if not at least I have it written down somewhere I can check when i inevitably forget what to do next time i reinstall!