Yes, opening the window if the air is cooler is a good idea. Computers do better in cooler temperatures... early computers were kept in very cold conditions, and most still at 72 F or lower.

Buying a notebook is better. Laptops are notorious for overheating, ruining the electronics. A notebook with Centrino inside helps it run cooler, too.

Raise the feet. I guess you can add small stick on footies to make the ones on the computer taller, giving more space for the fan etc. Be careful about putting it on an angle though, too much of one and it might shut off also (such as lying in bed with it propped up a the back to read the screen easier.) Never use one on a cloth tabletop or bedspread etc, (or a lap!) but I'm sure you know that.

You might need to look at the list of "processes" actually occurring at any one time. You may have many things running in the background that you no longer use or want. Deleting them will help your computer work easier.