My host is WinXP and my guest (on VPC 2007) is also WinXP. Both have SP2. I am unable to ping either from one another. However, I am able to connect to the Internet from the guest. My intention is to be able to connect the SQL Server on the host from the Management Studio installed on the guest. Right now I am using Shared Networking (NAT) on the guest's settings.
You want to use Bridged networking. This way, both the host and the guest will talk to your router/LAN to get an IP address on the same subnet.
With NAT, the host is acting like a router, and all you VMs are "behind" it on their own private network.
EDIT: Sorry, I was using VirtualBox terminology. As harrymc said, choose the card you have, not the other generic choices. I was able to ping out from an XP guest to the XP host, and from a Win2K guest to the XP host; from the XP host to the Win2K guest, but not the XP host to the XP guest. Then I turned off the firewall on the XP guest, and then that worked too. So there's also a firewall configuration issue, which might be handled automatically when you install a server program on the guest. But since you intend to go from the guest out to the host on the server, it may not matter.
As a first troubleshooting step, you can do an