How do you write protect a usb flash-drive?
Most USB drives have a small write-protect switch/slider which
you can use to make the drive read-only. If your drive doesn't have
one and its essential for you, then consider buying one that does
have the write-protect feature- USB drives are quite affordable
these days.
You can buy this software to write protect a pen drive:
penprotectorenglish.wordpress.com
There are, however a few things you can do, like ... * Secure
your thumdrive with TrueCrypt
* Use a Registry Hack to Disable Writing to USB Drives *
PenProtector - write protect a pen drive from viruses etc..