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