There seem to be a lot of SE referrals as to how to erase data from a Treo 700w. The easiest way is to do a hard reset, where you hold in the red power button and press and hold the reset button (under the pattery cover) at the same time. Your Treo will start to reboot, and you’ll be prompted to erase all the information.
This will reset your Treo back to factory settings (if you installed the update with MSFP, this will be retained). All e-mail settings and messages, any thrid party software, etc. will be wiped. Information on your SD card will not be touched.