This page has the following script, as well as everything you could ever need to script for HPL2, please bookmark it in your browser for future reference. To help navigate the page, you can use "Ctrl+F" to find what you need:
http://wiki.frictionalgames.com/hpl2/amn..._functions
I've taken the liberty to search for the desired script for you:
void StartScreenShake(float afAmount, float afTime, float afFadeInTime, float afFadeOutTime);
Shakes the screen.
afAmount - intensity of the shake
afTime - duration of the shake
afFadeInTime - time in seconds until full intensity is reached
afFadeOutTime - time until screen is back to normal
Also, if you just copy and paste everything, you will never learn; it is like having someone learn to read/write for you. My suggestion is to play with the different scripts and float values (which are decimals) until you become comfortable enough to use it in your story.
I rate it 3 memes.