It was a thermal pad, but it was no match for a credit card
Cheers for your help all, you were excellent. I got my heatsink off (eventually), got it clean (eventually), and then got it back on again (eventually). Added a back mounted 120mm fan, and added two fans onto my hard drive (although that biatch still says its running at 58*, which I strongly doubt as its reasonably cool to the touch). Now all I need do is take the front of my case off, when I find out how, and add in an 80' to complete my cooling upgrade. I'm amazed at how cool my CPU is now running with this AS5, idling at around 25, and on load doing about 32.
Thanks again folks, you're help has been A* quality.