I hope I'm not doing anything illegal when telling how to change the registry, but I doubt you can implement any "hacks" in there, since RO only saves hotkeys, setup configurations etc. in the registry.
But IF this is illegal, post down there, prepare to get modded!
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I found out, when changing some keys in your Windows registry, you're able to set every possible resolution. For example this one (should be 1000x400):

Yeah, I might say, you better shouldn't do this if you don't know much about Windows at all, since you can screw up many things when changing the Windows registry.
But I'll tell you anyway how to do this, since it COULD help with your problem.
(I hope you have a task bar somewhere, because I can't see it in your screenshot, lol)
Click on Start -> Run... -> Type in: regedit
Okay, now you have to look for the RO configuration. Mine is saved here:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Gravity Soft\Ragnarok
I'm using Windows Vista 64-bit, so you probably have to look somewhere else (I've never seen that Wow6432Node before @_@, must be 64-bit OS specific), but I'd suggest you to use the search: Press F3 and look for "Gravity Soft" or "Ragnarok". Go on with the search until you find the "Gravity Soft\Ragnarok" folder. Now your screen should look a bit like my screenshot.
Look for the key
HEIGHT. Double click on each, click on "Decimal", NOT "Hexadecimal" or "Binary", and change the value to 600 or 768 and press ok. Now look for
WIDTH, do the same things ("decimal") and change it to 800 or 1024, press ok.
DO NOT CHANGE ANYTHING ELSE, I can't guarantee that you don't mess up the game if you not only change the two keys I named.
I don't know if that works, but it's worth a try, I think.
