I have no idea why someone would give you a reference to download Premiere Elements 8 Content (Movie Themes, Disc Menus, Title Templates and the like) when you are seeking to install Premiere Elements 8, the program itself. Please be advised that you do not download and try to install Premiere Elements Content until after you have installed the program. After you install the program, the link to the Content would be used if you want Content beyond what the program installation includes.
Did you purchase Premiere Elements 8 as an online download from Adobe. If so, you should be able to locate it at
Adobe http://www.adobe.com under "My Orders"
Go to that web address, sign in, and in the Search field type "My Orders" and find the Premiere Elements 8 order which should have the download installation file option nearby.
Please let us know if you did purchase the serial number as an online download from Adobe and if you found the Premiere Elements 8 installation files to download again under "My Orders" at Adobe.
Looking forward to your results.