Running 2 GPU's Makes Both Run As Slow As Only Running One

[jamesBonds]

I have just begun to mine bitcoins, and am using the BitMinter client and group pool to do so. I'm encountering a problem with making the 2 AMD Radeon 7950 graphics cards run at maximum capacity when I run them both at the same time. If I just run one, it will normally run at around 400 to 420 Mhash/s. But when I turn on the second GPU, both only run at around 200 or 210 Mhash/s. How can I fix this using the BitMinter GUI? Also, I'm doing this at college so power use is not a problem; can anyone give me suggestions for how I can use the most power to run the GPU's as fast as possible? Forgive me for any clumsy misunderstandings with how I view how mining works, I'm hoping to learn much on these forums.