There are numerous posts about DWF Viewer blocking installations of current Autodesk products and that Internet Explorer 7 is required for Revit 2010/2011.
Just an FYI, the DWF Viewer does block the installation of Inventor 2011 as well. The trick is that you can install Inventor 2011 with Internet Explorer 6 but you need to have Internet Explorer 7 for the installation of Autodesk Design Review and Vault.
This means that you need to install Internet Explorer 7 or higher on your computer.
This is valuable information, I've just struggled for 3 days only to find out that VAULT 2011 will not install without Design Review and Design Review will not install without IE7 or later.
System Recommendations for Inventor 2011
Other Requirements: