The video card only thing is a myth, as long as the are PCI-e slots they will work with any card , sound, raid whatever.
I have a 3805 in my P5K-e (P35) board which is in a PCI-e16x slot (although its electronically 4x) and it works perfectly fine.
The video card only thing may not be a myth... I have an Asus M2N-SLI w/ 2 PCI-E x16 (one, I think wired at x8) and one of two things happen when I install my new Adaptec 5805 controller - no RAID BIOS posting, no device shown under Vista; or, POST hangs when the RAID BIOS presumably should be loading...
My 3ware 9690SA does the same thing...