I have an identical problem with a certain game (granted, not on a spanking Hitachi LCD, it's on a CRT).
I'm of the impression that it's a WinXP thing, though I could of course be horribly, horribly wrong.
It's waaaay too dark, and no matter what changes I make to settings I can never increase the brightness, yet every other single bit of software is fine.
Why not manually adjust the monitor's brightness? Well, it's old and already at max!