The Options Menu in Ilium Software Screen Capture lets you choose which key to press to take your screenshots. This menu will have different choices depending on the device you are using:
Windows Mobile Professional or Classic (Touchscreen / Pocket PC):
You will see key choices called Button 1, Button 2, and so on. All possible hardware buttons are added to the list. However, the locations of these buttons vary on devices, and some may not even be present on your Pocket PC. To find the correct button, you can select a key, then test by pressing buttons until a screenshot is taken. Turning your device's sound on can help, because you will hear when the shot is taken.
Windows Mobile Standard (Non-touchscreen / Smartphone):
The key choices you can use are the pound sign (#), asterisk (*), or one of the numbers on your keypad.
Whenever you press the button you've defined, a screenshot will be taken and saved to your My Documents folder, until you stop the program as described here.