My computer's the same there's no outside knob or control for it. Mine's a Toshiba and there's two little Toshiba Function keys over F6 and F7 to control Brightness but you might not have those. I don't know what it's so insanely difficult to change!
You're running Windows XP?
You'll have to go into your Control Panel, and look for some sort of Graphics Controller. Mine is called "Intel Extreme Graphics Controller". Once you've got that open you can change pretty much everything you want. Trouble is finding it.
I couldn't find any 'Windows' based program to change it... does anyone know if there is another way?