I have two computers sitting very close to each other. 

One is an older computer nearly constantly logged in via VPN to another network, and I use SVN to push/pull files from that other network and use a few other resources.

The other computer is my main development computer, and I prefer to keep it unconnected from the vpn.

What I would like to do is connect an external hard drive to both computers concurrently. As it would be seen as a physical drive on the system, the computer that is VPN'd in would still be able to access the files (update them from SVN, etc.) and the second computer would be able to use them as well. 

Any suggestions? I don't think I can use a cheap NAS because the VPN locks out all network access (e.g. I cannot access the second computer). And I have yet to find a hard drive that will allow two computers to be connected at the same time.