For usb support you need to get the PUEL version of virtualbox from their website.
As for connecting machines, that is a bit tricky. You will have to use the "Internal Network" option, choose a name for that network, and make sure you choose that internal network on all of the machines you want to connect. They will have no access to the internet this way, unless you choose to use 2 network cards, one NAT and one for the Internal Network. Not sure about that, will have to check.
Update: Checked, and it is not working.
Last edited by ultra magnus; 1st July 2009 at 06:54 AM.
Reason: Checked some things.