I have VS2010 with SP1 installed on it. Still I am not getting VSIX project template in “New Project” dialogue box.
I have referred following question too but no luck
Can't find VSIX Project Type in VS 2010
Any clues?

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Make sure that you’ve installed the Visual Studio SP1 SDK – available here.
That has the proper templates you’re looking for
EDIT:
Check
<drive>:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\Extensions\VSSDK\— that’s where (I think) the extensions should have been installed to. You should see a number of sub directories. See if this matches with your install:If that file’s not present, it would suggest that something went wrong with your install of the SDK.