virtualbox.org

I have two VM's set up under VirtualBox 3.0.2 - XP and Windows 7 RC. Both exhibit slow & inconsistent network communications, whether both are running simultaneously or only one is up. I noticed that both have leased the same IP address from the VirtualBox host, but that's not the problem since the slowness does not occur only when both VM's are up. On both VM's, pings of the host or a server in my LAN get a lot of time-outs, and usually fail to communicate successfully. It doesn't matter whether I ping by IP address or NetBIOS name or FQDN.

Appreciate any suggestions.

Try switching the Virtual Network Adapters to the IntelPro/1000 T Server and see if this helps your problem.
This is done in the guest settings.