I would suggest putting it at the side of the computer.
For my laptop, I use something like this:
It cools my laptop down significantly.
If you don't know what that is, this google search should help:
LinkThey can get a
little expensive but it's worth it.
As for your question, basically the more the processor has to work the more heat it will give off. I wouldn't say '
how many windows open' but '
how many Large Programs or Games are open'.
**Large programs can include Image Processing software (such as Corel Draw or Macromedia Flash).