Same issues with the built-in NIC not supporting Jumbo Packets so you still will require the Addonics card (or Linksys EC1000, etc.)

Thanks,
what about RAM?
Any advantage getting 4GB for DVR?

The advantage of a larger RAM buffer decreases as you add more processing power. So especially with these new machines running at 2.6Ghz or faster, 2GB will be plenty of RAM.