I have started a discussion on a Microsoft forum regarding some 32-bit SDK calls in applications which you may (or not) be interested in, because I have recently had an issue installing PI-Datalink and getting it successfully working.
It's to do with 32-bit applications looking in the wrong location, and i'm wondering if OSIsoft have hit the same problem, becuase the workaround i've applied is to copy the PItrendXL.xla into the 64-bit path to make it work.
There has been some response from Microsoft, but it's not very convincing at the moment. My suggestion is to avond running 32-bit applications on a 64-bit platform to avoid data manipulation by windows. Please view the discussion.