HowTo Share a USB Hard Drive

I have installed a couple USB 2.0 hard drives on systems in my home network. I have shared the drives via Windows Sharing and Security and they show up as available shares on the LAN in both Windows and Linux Samba. However, I cannot mount the shares in either OS or even view the contents. All I get is:
\\SYSTEM\Drive is not accessible…

Is there a setting I’m missing, or a registry setting I must change? How can I share a USB volume?