|Ping the other computer's IP address to make sure it is not a layer one issue, then ping the computer's name to make sure it is not a three issue. |
Try using UNC pathing by doing (Windows Key)+R to bring up Run and typing \\computerb\shredfolder to see if you get access that way.
Check the Local Area Connection in your Network Connections...
XP : Control Panel -> Network Connections -> Right Click -> Properties.
Vista : Control Panel -> Network and Sharing Center -> Manage Network Connections -> Right Click -> Properties.
Make sure "File and Print Sharing for Microsoft Networks" is in the list of "This connection uses the following items:".