I had an 8800GTS in this PC before the 5830. I first put the 5830
next to the 8800
in the case, assuming it would work. It performed all normal operations fine, displaying my second monitor with no problems. I installed the drivers and SDK, but when I would try to open phoenix or guiminer they would forcequit. I did some research and found that cards of different chipsets don't get along in Windows 7 (weird). So I took out the 8800, which had been mining successfully until I put the 5830 in, and removed all the nVidia drivers.
notes: computer restarts were done between all driver/hardware changes
I re-installed the APP SDK and latest drivers for my 5830 just to be sure, then tried guiminer again. I got the message "No OpenCL devices were found," and that is where I am now. I should mention that when guiminer was forcequitting when both cards were hooked up, it did not display an error message. I'm sure a real solution exists besides reinstalling windows, which I am hesitant to do because this is my main computer.