I registered just to post this
I just put a 5830 into an old foxconn nforce4 sli mobo I had laying around. It wouldn't post. Just no signal to the monitor but all the fan's were spinning and such. According to my research some nforce4 motherboards have an updated bios that allows PCIe 2.0 graphics cards to work other companies didn't do the update.
On a side note I had spent a good portion of my free time during the day cleaning dust out of the case and moving hard drive's, did a fresh install of the OS (with the old graphics card in it still) tracked down some extra fans for more cooling and THEN put in the 5830. If i had only tried it first to see if it would even boot.
Bah! So much for PCIe 2.x being backwards compatible with the older slots.
If you get lucky and have a bios update that lets the 2.0 cards work with the mobo turn the chip around so its in "sli mode" it really just activates the 2nd slot.