Now add a new DWORD called WriteProtect and put the value as 0 to disable write privileges to the USB port. To reverse the step, either delete the WriteProtect REG_DWORD or toggle the value to 1 which will enable the port.
Remember that the above trick works only with Windows XP SP2.
If you like to go a step further and disable users from connecting USB storage devices to their computers, here’s the trick:
Open registry and navigate to the following registry key:
Now in the right pane, double-click Start and type 4 in the Value data box (Hexadecimal) and quite the registry editor. To enable the USB storage devices, change the Start value back to 3.