Setting up a Custom Resolution In Windowed Mode
If you're running EVE Online in windowed mode, you may want to fine-tune the size of the client windows. You can simply select a different resolution in the in-game settings, but you may find they're too small or too big, and don't make best use of your screen real estate.
To set up a custom resolution, try a program like SwitchResX. Enter the screen-size you want in the Custom Resolutions tab. Doing this won't change the resolution your monitor is running at, but it will let the EVE Client see it as an option next time you play the game.
External Links
The Macintosh Thread on the official forums.