24" Inch iMac overheating

I just touched the top of my imac screen... above air vents on top and burned myself... how hot should an imac run?
i dont shut it down at night it goes into sleep mode...

any suggestions?

http://www.microdirect.co.uk/(28997)LG-GGCH20L-BluRay-HD-Combidrive-Black-SATA.aspx
also how do i go about getting a dock for this?
I want to plug it in externally using usb or firewire or am i out of link?

It isn't overheating. If it had overheated, it would have shut down automatically as a protective measure.

As far as the drive, it would be much easier and probably more cost effective to just get an external drive. Here's one, for example