Ok guys, I agree with the aproach that always depends on wich part of the machine are you using it often, besides thinking that is a machiine tha's at least has already 6 years old and if it's your primary computer you may have been experience a lot of issues if you don't take care of it with regularity. You have to gave it at least one full service once every 12 to18 months.
Those machines can warm up like !@#$ on earth depending on wich OS you have installed on them, if you have enough RAM to run your Apps, remember that the Apps evolve quickly and they're thirsty of power, if you have Lion installed and 2 to 4 GB of RAM and tried to run Adobe CS 5 - 6, core gaming, 3D rendering or something like that. Then may be PART of the problem (just part of it).
Besides, if the computer has a Mini DVI to VGA adapter all the time giving video signal then you are forcing the proccessor, the video proccessor making a video out signal, then converting the digital signal to analog (remenber that you're asking to the MacBook to gives VGA signal "thet means convert the digital signal to analog"), proccessing the data throught the I/O chipset and then to the port, all that without taking in count all the other ports connected, remember that the USB and FireWire ports give electrical power, so consider all that is plugged.
Be prepared if you are going to connect a SSD instead of your optical drive and use it as a startup disk, I will connect it in the place of the original HD and the HD in the place of the optical drive the SSD will heat pretty much too (not as the HD, but it will be more than warm).