Not sure how comfortable you are trying these, but I researched some of this:
Disable IPv6. Make sure the Windows 2008 server is only pointing to internal DNS servers. Disable TCP Chimney, TCP Offload, IP Offload, TCP Checksum, and IP Checksum.
SBS 2003 CAN be on the same network as 2008 if 2008 is not SBS. I think you said it is just Enterprise, correct?
