Detect if something is Running Full Screen

I have a program, that alerts you by showing a form in the bottom right corner of the screen. The only problem is that when there is a fullscreen app running(ie, a game) it minimizes it when it shows the alert.
How can i detect if there is something running full screen so i can disable the alert when im playing a game...

This is kind of IM program like Skype or MSN ?

It isnt a Chat Program, but the pop up is exactly like MSN's little alerts...

Bump! :)