Missing camera error in iMovie. Can I reattach the missing files from a different location?

I am new to the world of Mac computers and so far am not off to a good start. I imported video files from a memory card onto my computer to edit and later upload to youtube. After hours of editing, I ejected my memory card to find that apparently I had been editing the files on the card and not the files that were copied onto my computer. When my memory card is ejected, all of the video files are blank and say "camera missing".

Is there a way to reattach or relocate these files so that I don't have to re-edit all of my footage? When I import the same files (the ones copied onto the computer) into iMovie, it treats it like a different event and does not "replace" the missing ones.

Is there another way to share/export this movie? When I try to share the movie (with the memory card still plugged in) it says that I can't because its still attached to the camera. UGH!

I have scoured Google and tons of discussion boards to find an answer to this problem but have found nothing.

Hopefully this all made sense... please save me from having to re-edit the entire movie!

Thanks in advance