There are other articles that explain this but finding the files for this can sometimes be a problem. Basically the usb does not work directly, software drivers need to be installed on the machine that you want to use to charge.
These drivers can be downloaded here ...
http://ofg.osnn.net/razr/
The detailed article for the same can be found here
http://www.somelifeblog.com/2007/02/motorla-razr-v3-charge-via-usb-on-pc.html