Thanks for the comments. The appearance of the screen (i.e., somewhat darker at the top) isn't due to "poor viewing angle", such as if I were to view it from the side or from above; this gradation is apparent when I'm looking exactly perpendicular to the center of the screen. So is this problem inherent to TN technology, or is it perhaps due to some other reason?
Your comments on color fidelity are appreciated. I'm actually more than satisfied with the color quality the HD2200 provides, at least for my photo purposes, although I realize that publication-quality usage may require something better.
When you're looking "dead on" at a large screen, only a small part of the screen is actually perpendicular to you. The edges of the screen will be at an angle to you.
It could also be that you have uneven backlighting, though.
But I agree with the other posters that a TN film panel is a poor choice for photo editing in any situation. Sell the 22" panel and get a decent 24" SPVA or S-IPS panel instead. Once you go 8-bit, you won't be able to go back.
Wind, Sand and Stars.