how to display a form without destroying a game?

i'am creating one application similar to winpopup when i type something over here then it will appear in other pc's. my problem is when somebody is playing game like fifa 99 and other the program will minimized the game and show the msgbox.. it's ok but when they tried to maximize the game again the whole thing goes grumbled.. and the game will be destroy.. hope someone could help thanks...