Welcome to the forum.
All Imported media files are stored where they were, when Imported. They are NOT in the PREL (Project) file, and PrE does not move them. See this article for more detail: http://forums.adobe.com/message/3397716#3397716
Where were they, when Imported?
I read that post you made, and thanks so much for responding.
I understand that the projects link back to the original video file form the import, so the project files themselves aren't large. I was curious about this and was checking my HDD storage capacity during my project editing. When I started the project, I had about 16.5GB of free space. After I had edited a few clips and deleted others, I checked again and my HDD was at ~14.5GB. I assumed that meant that my tinkering had resulted in Adobe making temporary video files and that was what had taken up my HDD space. So I was confused as to what had happened. I noticed that some of the space has now returned since my original post, but I'm not sure why that 2GB was lost.
I should also mention I haven't downloaded/changed anything else on my HDD during this time.
Thanks again for responding Bill!
Well, when one Imports Video files, with Audio, there ARE some extra files, that are created. See this article for more background: http://forums.adobe.com/message/3892177#3892177
That might fill in a few of the blanks.
If not, do not hesitate to ask for clarification.