When you install Office Web Apps on windows 7 that has Sharepoint 2010, you will see following error message
Setup is unable to proceed due to the following error(s):
Windows Server Features or Role Services required by this product are not enabled.
For a complete list, refer to the link below. For the list of pre-requisites needed to install the product please refer to:
Correct the issue(s) listed above and re-run setup.
You can install all required prerequisites for this product by selecting the ‘Install software prerequisites’ option in the splash screen. See Help for more information.
This is because Office Web Apps can only be installed on a server operation system. Office Web Apps can only be installed on Windows 2008 Server x64 SP2 or R2 now. Also keep in mind Office Web App can only be installed after SharePoint Foundation 2010 or SharePoint server 2010 is installed.