It will show all of the cards in device manager, CPU-Z, and a brute force program I have, but catalyst 12.1 will not detect it. I have not removed and reinstalled catalyst to see if it will recognize the third card. The issue I am having is I want to make a liveUSB for the machine like I had before I added the 5870 in there. Regardless of what I set the boot options to I cannot get the thing to boot into the operating system. I'm not sure what the issue is?
I don't have Windows at home so I cannot help you with that, but it sounds like what I've read in the forums: Windows' Catalyst drivers won't see it.
Some BIOS vendors won't let you boot from a flash drive (yes... in this day and age). Maybe you can try this if you have an optical drive http://www.howtogeek.com/howto/16822/boot-from-a-usb-drive-even-if-your-bios-wont-let-you/
(However this is unlikely... look for USBHDD - it can also be in "HD boot options")
I may end up giving that a try. The issue is that I had a boot USB for the computer before I added the 5870 that worked fine with the boot parameter xforcevesa. Now, with the 5870 it will not work and gives me an MSI-x error of some sort. The bios and everything, but the 5870 is the same.