I would try unplugging both 500 GB hard drives and setup the two 250 GB drives in RAID 0, then pull out one of the video cards so that there is only one card plugged into the main PCI-E video slot. Then try it from there.
On my system, for some strange reason, Windows 7 WILL NOT install if I have more than one hard drive plugged in. Once I unplug the second hard drive the install goes very smoothly.
Try what I've suggested and see what happens. Leaving the two HDD unplugged and installing to the two 250 GB HDD. If the install works, then after you're up and running plug the other two back in.
If that still doesn't work, it may be the motherboard.
I am very partial to Gigabyte motherboards. Great quality and tons of features.
I wish you luck on this, I will try to search some more info, but in the meantime I'll be at work till about 10 PM CDT USA.