Dual Monitor screen brightness issue

Having an issue with my main rig with screen brightness. I have a pair of 28" monitors, one connected with DVI and one connected with HDMI. Both run into my primary videocard, which is a EVGA GTX560ti. I have 2 of those as well, but they are normally NOT running in SLI.

The issue is that my primary monitor is much brighter than my secondary monitor. The secondary is so dim that often it is difficult to read things on it. Now obviously I could easily resolve this by increasing the brightness on the secondary monitor, but here's the rub. I dual boot this rig with XP home 32 bit, and in that OS both monitors are exactly the same brightness. Any ideas on this?

3770K CPU
ASUS P8P67 Deluxe MB
16GB Corsair Ram
(2) EVGA GTX560ti video cards
SB Audigy ZS sound card
WinXp Home 32bit
Win7 Pro 64bit

Any other information you need just ask...

Thanks in advance!!