The trick of the day is to prevent the user of your pc from writing data to the USB drive.
the steps follows:
for this to happen you just need to make some changes in the registry of the pc.

1. Go to Start–>Run.
2. Type Regedit.
3. Navigate to “HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control”.
4. Here, add a new folder on the left pane by right clicking on it and selecting “New–>Key”.
5. Name this folder as “Storage Device Policies”.
6. Right click on this folder and select “New–>DWORD value”.
7. A new entry will be added in the right pane. Rename this entry as “Write Protect”.
8. Right click on this entry and select “modify”.
9. A window will be poped up. Enter value “1″ in the “Value Data” option and click ok.

Now your pc is protected from writing any data to the USB drive.

For allowing the writing follow the above steps and enter value “0″ instead of “1″.