After a great experience upgrading a single CPU 4.1 to 5.1 six core 3.33, I now have the opportunity to upgrade a dual CPU 4.1. Firstly, it's only because of this forum and the helpful information available here. Very little is out there on the subject of "Delidding". So, I am going to document my experiences here. I started by research and observation of others pulling, heating, hammering, cutting and prying the IHS (integrated heat spreader) from the CPU for proper spacing between the mother board and heat sink. The difference in the dual CPU 4.1 is they are held in place solely by the heat sinks screwed to the mother board. The heat sinks are smaller on the dual units and I believe that Apple ordered the Xeons liddles to compensate for the lack of cooling. I have an old Xeon Chip from a previous upgrade that I have used for practice and the results have taught me that cutting the seal from the IHS is the easy part. I used the old style single edge razor blade to cut just deep enough on all four sides. By drawing a line on the blade as a depth gauge I avoid cutting too deep and damaging the small caps inside. Using two thicker box cutting blades, I inserted one on each side between IHS and PCB then rested the blades on small wooden blocks and evenly applied downward pressure to the chip. Way more pressure was needed than I had expected and am certain that I had damaged the CPU at this point but who knows. Maximum operating temperature of the CPU is 172 degrees so I would assume that I can safely heat the IHS to this temp without causing damage while softening the thermal paste for separation. Also, I wonder what solvents can safely be applied that may simply dissolve the paste for the easiest removal of all. The goal is to avoid installing new CPUs with the lids on/avoid the issues that pertain.