Hi, kelean, and Gang,
The Delll Latitude D800 typically runs a Pentium M CPU - under normal conditions this unit should not overheat. Are you saying the overheating problem is peculiar to PCLinuxOS? What temperatures are you actually experiencing? I see no mention of it, but is the unit shutting down on an overheat problem, or are you just concerned that the fans are not running?
The fans in the unit should spin up briefly during POST and then only run when needed to cool the CPU. If you don't hear the fans spin up at all, even during POST, yeah, be worried. Otherwise, look with a monitoring utility like the Hardware Temperature widget and see where the temperature is running. If you're below 120 deg F (48 deg C), the fan may be running only whisper-quiet. At no-load, this CPU should run about 110 deg F or cooler. (You may need to put an ear by the heat exhaust to hear it running.)
Setting up cpufreq is good advice - it will let you control the system a bit better.
It's premature to talk about hardware problems here - looks like this might be software-related, but at least check and see if the unit has sucked up a lot of dust. That can muffle the sound of the fan and make it cool less efficiently. A good blowing out with some canned air might improve matters a bit.
Just for reference, here's a link to the D800 Service Manual
. It may be of help in locating components. It looks, from the manual, like the fan on this unit is designed to be removed easily for cleaning.
In fact, it looks like this unit is simply and ruggedly designed, and the motherboard is the same as in the Inspiron 8600 and the Precision M60, which indicate a pretty good lineage for it. It should run any Linux distro, and PCLinuxOS in particular, very well.