Pre9 has two installers - one for the Core Application and second for the content(or templates.)
"Adobe Premiere Elements 9 Content" files contain SD and HD content i.e. movie themes, DVD templates, title templates etc
Pre8 also followed a similar structure, only difference being that in Pre8 when the content installer was run it installed the entire content (HD and SD)
With this release, adobe has split the content into different installers. (SD Content 1, 2 and 3 and HD Content 1,2 and 3)
Installing the content is optional, you may skip running the content installer or run it later, and it shall have NO effect on the normal functioning of Pre 9.
Great, thanks! Awful lot of file space just for templates...
That is one of the reasons that the program (+ content) comes in two files - users have the option of NOT installing the additional content. Other than not having access to the Menus, Themes, etc., the program still functions just fine.