From the Treo 800w User Guide:
Using Auto-Keyguard and Touchscreen Lockout
Auto-Keyguard
lets you automatically lock the keyboard after a period of inactivity.
1.
Press Start and select Settings.
2.
On the Personal tab, select Keyguard .
3.
Set any of the following options:
Auto-Keyguard: Set the period of inactivity that passes
before the keyboard automatically locks or before the
auto-keyguard feature is disabled.
Disable touchscreen: Set whether the screen’s
touch-sensitive feature is enabled during a call. If you
disable the touchscreen, the Touchscreen Disabled
icon appears in the lower-right corner of the screen during your calls.
4.
Press OK .