I finally got PDFs to work in my browser by doing the following.
1. Uninstalling Reader version 9
2. Installing Reader version 8.1 from the abobe.com website
3. I then had to uninstall via control panel add remove programs the adobe.com program, and I also uninstalled the Adobe AIR program.
4. I then checked in my Add Remove programs list and Adobe Reader 9 is still listed, I uninstall it again (why I don't know).
5. I then view a PDF file outside of Internet Explorer and I have to accept the license agreement in a popup window to get Reader 8 working properly.
6. I then go to a web page that links to a PDF file and finally I can view PDfs in the browser again.
We have around 30 PCs in our department with Adobe Reader 9 and some of them work in a browser and some of them do not, so there appears to be a conflict of some sort.
For info, I have Acrobat Professional 8.1 on my PC also.
Good Luck
ScottJ in London, UK