If you put the 250 gig in as a slave drive then you won't
lose anything off of the drive itself, but you will have to reinstall
your programs and applications to the 40 gig so that windows
will recognize the applications. For instance, if you have
microsoft word on the 250 gig and you make it a slave drive
you will have to reinstall word on the 40gig so windows will
recognize that you have word installed. The documents created
with word will still be on 250 gig. Your pictures, music etc will
still be on 250 gig.