Copy wma files to iTunes

I have a massive wma and mp3 library on my computer and I just bought my wife
an iTouch. I've witnessed her dragging my music files into her iTunes library
and I'm not sure if that's removing my music directly from my folders and
replacing them with aac files.

Is it safe to simply drag wma files from my folder into iTunes? I'm not
worried about duplication since I have a large harddrive. I just don't want
to lose my wma files.

Is there a way I can protect my wma files from deletion by other users? I'm
running Vista Home Premium and I have setup separate user accounts. The music
files are all stored on a separate internal harddrive.