I have the same model of notebook, and I run dualboot Windows 7 and Fedora Core 15 on it. I struggled for the last year with overheating (it would actually shut down in BOTH Windows and FC) and tried all sorts of software solutions and fan controller setups, even pulling it apart to clean the fan. Some improvement, but problem quickly recurred.
When I pulled it apart to clean it for the third time, upon putting it back together it wouldn't run for more than five seconds. I realized that taking it apart that many times had disengaged the thermal paste from the cpu core, and so it was overheating instantly.
I bought some new thermal paste, cleaned the CPU and heatsink, applied the paste and put it back together. Now, ZERO problem. Not a single overheat, it runs sitting on carpet, with the carpet blocking the air intakes, WHILE it runs benchmark software for the CPU and GPU.
It's my opinion (as a BSc Computer Science student on the brink of graduation) that the thermal paste used at the Dell factory is awful quality, and should be replaced with some decent paste.
Hope this helps.
Here's a youtube on how to correctly dismantle the notebook and how to apply thermal paste..