XP SP2 can support a registry key to write protect USB block devices such as memory sticks.
It has been introduced to allow sys admins to block USB memory devices to prevent data theft.

I created a small systray utility for this (including reboot. Necessary for enabele write protection) called USB-Blocker.
Windows XP and Service Pack 2 detection included !!

Give it a try.

You can download a copy here .

For questions and/or comments mail me.

Greetings from the Netherlands.

Robert