I have a ThinkPad running XP. When I use the USB tether to connect a new BlackBerry Bold, the laptop doesn't see it. Neither Verizon's Access Manager or Blackberry Desktop detects the device. Other the other end, the Blackberry cannot be charged by the laptop. The cable itself is fine and allows the Blackberry to be charged via a wall outlet adapter. I have not being able to get any help from Blackberry or Verizon.
Try a different USB port. Sometimes they do not offer enough power through the port. Same issue if you are running through a hub.
I get this in the car, that the various car chargers I have tried often do not offer enough power.