Leaving Lid Closed while using attached CRT/Mouse/Keyboard

Hello,

I've set up a poor man's port replicator on my desk. This allows me to use the CRT monitor and a full size keyboard and a normal mouse. I was wondering if it's safe to keep the laptop lid closed during this time, even while playing intensive games. I don't want to overheat the LCD or something. For now I leave it open a couple inches.

Thanks for any replies.