I've always noticed that with UT, OGL runs better on my system than D3D (150fps vs 50), and it's darker, however if I have my brightness all the way up inside the game it looks just fine, I'm assuming you've tried that already, but if not, give it a go.
But other than that, I've never come across a fix or anything specifically for the brightness. A friend of mine had a monitor that was dying out and EVERYTHING was dark as hell.
Are you using the new catylast drivers?? if so there is a tab for game gamma you could try that ......... I also like powerstrip for that you can make a profile when you click on the destop icon to open the game ( any game) it will set a costom display profile ............ of course you need to make the profiles for each game not all of them need let's say 250%+ brightness
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS