Originally Posted by Crimesy
You can manually wipe the device by entering the password incorrectly x times (usually 10 times) or via the Options/Security menu - there should be an option to Wipe Handheld.
Another way to wipe the device is to use the desktop manager, input the password incorrectly x times to force a 507 error and then re-load the software. Make sure you have an up-to-date copy of the device software first though.
This seems like a bit of a long way around. As JS said there is a wipe handheld feature built into the device.