You can also play at other than supported resolutions, by editing the config.div file (in Notepad or another text editor). At 1152x864 (if you set the game resolution the same as your desktop resolution) the border around the auto-map will not line up properly, but that is just cosmetic. This is what I did, since I found the text a little small at 1280x960 and I wanted a bit more visibility than 1024x768. At too much higher than supporter resolutions, though, opening the auto-map can cause the game to crash.
BTW, the inventory and skill window hotkeys are toggles, so if you hit 'I' or 'S' a second time (without selecting a different character) it will close the corresponding window.