For the longest time I have not been able to open up a PDF in an IE7 window. It was driving me crazy! I can download the PDF file and then open it, but this is an extra step or two I'd rather not have to do. Today I found the solution! At least for Acrobat 6 (I don't know if the same work-around applies for Acrobat Reader). Click on Edit>Preferences>Internet and then uncheck 2 boxes: "Display PDF in browser", and "Allow fast web view." Works for me!