Gslide, as you were told before you won't achieve a level of brightness equal to any decent LCD with a plasma, that's just how the technology is. BUT you get great contrast, hence great blacks and a far more faithful color reproduction.
I think you need to stop comparing the two technologies side by side and focusing only on the whites' brightness, because, as they are, the whites on this screen are perfectly fine! Remember the last time you went to an actual movie theater, I don't think the whites were as bright as to blind the spectators, the whiter isn't the better!
Plasma technology excels in reproducing a movie_like picture, that's why it's the technology of choice for movie-lovers and home-cinema enthusiasts. LCD's, on the other hand, are derivated from multimedia applications and as such are great on still pictures (ie desktops...) and videogames (even though I love my xbox360 on my plasma) but have a more artificial feel to them. Of course LCD's can produce brightness as to make your eyes bleed, but what's the point?
Also I strongly advise you not to get into the service menu. Not only will you likely not be able to get brighter whites, but you risk messing up the picture for good, as apparently a number of posters here have.
My advice to you is to just enjoy your plasma for its numerous qualities and stop focusing on a flaw that isn't really one!