CPU and GPU overheating due to thermal pad decay.
The Dell XPS M1330, bought around May 2008, works great until after a period of time when the fan is dusty and the thermal pad no longer dissipates heat from the CPU, GPU and the chipset to the heat pipe. This results in the computer slowing down (mine goes from 2GHz to 780MHz, at load can range up to 80 degrees Celsius) after 5 minutes or so of load on the CPU.
While the problem can be resolved by a Dell technician coming in, this is an impractical solution once the warranty has expired.
It would be great to see a guide how to open and add/replace appropriate parts/products in the computer to ensure proper heat conduction from the chips to the heat pipe can do its job.
First, here here is the manual that allows you to repair it yourself and here is a link where you can download it might be easier to follow. If you check with Dell there are new thermal pads that can be purchased as well as check on here . Second, how often does it happen to you and where do you operate your computer if it happens frequently? You might consider a different environment for the computer. Good Luck