Unless it's the SLI part causing it, no. I have my PVR 500 MCE running on an A8N-E with an X2 3800+ and Win XP Pro & X64...........no conflicts whatsover. Tell them to D/L the newest drivers from the Hauppaugge site.
Did a bit of looking just now in some other forums and there are definately people running the 500 as well as other models on the Asus SLI boards with no problems. Do a hardware check also.........something is not right.....