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
16 GB free disk space to accommodate the installation files and temporary files created during the installation.
Microsoft Mouse compliant pointing device
1280 x 1024 or higher screen resolution
Internet connection for Web downloads and Subscription Aware access
Adobe Flash Player 10. Note: The multimedia learning components of the Inventor Help system, such as the Ribbon Introduction, Command Locator, and Show Me animations require Adobe Flash Player 10 be installed. If it is not already installed, you can download it from http://www.adobe.com/products/flashplayer/
Microsoft Internet Explorer 6.x through 8 (not true 7 through to 8)