I use third party Task Manager to manage running applicationon my pocket PC. HTC Task Manager is pre-installed on your HTC device. If you use third party PDA application to manage your running applications, You can disable HTC XButton / Task manager by following these steps:
1. At first go to start
2. Then navigate to Settings=>System=>Task Manager
3. Tap on Buttons tab and uncheck all check boxes.
4. Download Startup Manager . Then install it to your pocket pc. Go to start => Programs => Startup manager.
5. Go to Menu => Services Find and select TaskManager
6. Tap on action and choose disabled.
7. Then soft reset your device.
If you have MemMaid on your device, you can Use MemMaid after step 3. Go to “Startup Services”. Find “TaskManager” and change it to “Manual Start”. Then soft reset your device.