Windows supports and sees 4GB memory. The server versions support/see much more. The largest server configuration I've used has 96GB memory.

I believe the issue with Asus is the way they make their boards. I recently explored using an Opteron 170 processor as a test bed for a new server OS. I looked at the Asus boards extensively before determining that they don't meet the specifications for the OS product testing. The Asus web site clearly states that the 3GB limitation is because of resources in the south bridge.