I use Premiere Elements 3.0.  I’ve created many projects to edit footage from my DV camera.  I just discovered that PE creates cached media files, autosaves and other files that take up a lot of space!  Incredibly, PE doesn’t give you a way to delete projects you have saved so these extra files accumulate on your hard drive.  I found this thread on how to delete a Premier Elements project. 

You go to where your project files are being saved and delete the folders:

Adobe Premiere Elements AutoSave
Adobe Premiere Elements Preview Files
Encoded Files
Media Cache Files