Help with IPAQ RX3715
(1) LAST USED APPLICATION
Enable password protection. Start>Settings>Password
(2) SENSITIVITY / PRIVACY
Choosing "Private" prevents the appointment from appearing on your Today screen. I figured this out by creating two appointments for today and making one normal and one private. The private appointment is still viewable in the Calendar application, so if you want to prevent others from being able to access this, enable password protection.
(3) TODAY MENU
There is no way to do this using the software that came with the iPAQ. However, there may be third-party software that would accomplish it. I did a quick search that turned up nothing, but you might be able to find something. Try handango.com or pocketgear.com.