In testing out the new Windows 7 -beta in Virtual Box I came accross my first issue.
The default NIC driver that Virtual box adds to the guest VM was not working for me in Windows 7. During the install of Windows 7 I chose the option of "Windows Server 2008" as the OS Type.
Once installed I was able to get the network up and running by changing the Network Card to an Intel Pro 1000 MT Desktop adapter. Windows 7 then detected that card and installed the necessary drivers for it.
This may not be the only way to solve the network card issues but "Itfixed" it for me.
By the way, my first impression of Windows 7 is that it is very much like Windows Vista. I will have a more complete review upon further testing.