If you get the xw8600 QuickSpecs via a Google search you can look up any of the dual-core or quad-core processors for that motherboard and find that they all are LGA771 socket processors..... your X5460 is listed in those QuickSpecs and that is why they will work on your motherboard.
That is not a LGA775 motherboard. Those tab things won't work on these HP motherboards.... the motherboard looks at the sSpec code of the processor, which you cannot change, and if it is not on the approved microcode list it won't fire up (there are some very rare exceptions).
You need to read up on my post on how to spoof the motherboard of a xw8600 to think that is has a "Performance" heatsink and fan, I believe, because it is my understanding that the motherboard can tell if you are running processor(s) that are 120W max TDP or hotter, and wants to see the higher performance double fan double tall heatsink over each of those processors.
It is all in the forum.... you'll need dig a bit. You have the key words to search under now.