Hi Frosty120. I can't help with all your questions, but to keep the thead alive I'll answer a few points.
Running AV presentations and DVD'S isn't very demanding in terms of processing power, but I agree that a lot of RAM will help, so I think you should be loking for at least 512M.
Any well made laptop should have sufficient cooling for continuous running at full processor power.
The main difference between the desktop and mobile versions of processors is that the mobiles are designed to minimise power consumption, and I think one of the ways they do this is by throttling back the clock rate when they aren't busy computing. They do this mainly to get extended battery life. A side benefit of this is that they should also run cooler. If you are using the laptop mostly on mains power, then battery life is less important. Expensive top-end laptops tend to have large batteries which cost a lot of money, so you can make a saving there.
This looks like a useful device to help keep a laptop cooler click here