I agree with the other posters, I have a 43' Toshiba with a Playstation 2 and x-Box hooked up to it for about a year now and have had no problems.
You have to pause the game and leave it for a very long time to burn the image onto the screen. If the picture is always moving it's ok, and sometimes I have played games for up to 6 hours at a time.
Although when your kids start playing games on the big screen they WON'T want to go back to their small screen, trust me.
So it won't do any damage to your screen, but you might not be able to kick the kids of the TV again ... the choice is yours, but really give them a break , it's amazing to play games on a big screen Tv .... and I'm 29