Instructions
Purchase Xpadder from the official website. As of July 2011, it costs $9.99. Select any download location of your choice.
Open the folder to which you downloaded Xpadder. Right-click it and select "Extract Here."
Double-click the Xpadder executable file. Wait for the program to open.
Click the game pad icon, followed by "New."
Click each of the tabs, following the on-screen instructions. Each of these tabs will ask you to press the buttons as they appear on the screen.
Press the button you want to assign to a key. A layout of the keyboard and mouse appears. For example, press the right trigger button on your controller, followed by the left mouse button that appears on screen. This will map the right trigger button to the mouse button, which is for firing a weapon in "Half-Life 2."
Repeat the previous step with all button presses. You may wish to map the left trigger to the right mouse button, the "Start" button to the "Esc" key, and the face buttons to the "E," "R" and "G" keys, because this matches the console version of the game.