EDIT: On the issue of this possibly being "modding" thread, I was given permission to post this by one of the staff before I created it.
I ran a quick search on one of the registry entries required for this trick, so I'm assuming this hasn't been discussed here before. Another member told me about this last night, so I ended up trying it for myself, and the results were pretty spectacular.

UPDATE: The maximum resolution that Maplestory can support is currently 2048*1536. If one of your resolution parameters (either your game width or game height) exceeds this, this method will either glitch or default back to 800*600. To avoid that, be sure to set the game window's width to either 2048 or below, and the games height to 1536 or below.
UPDATE 2: Reported to no longer work. See page 2 of this thread for more details.