That's already been covered in posts below, Elisabeth, but again:
If QuickTime 7 Player didn't get moved to the Utilities folder automatically, you can install it separately. Insert the Snow Leopard install disk, go to the Optional Installs folder and run the Optional Installs.mpkg. You'll be able to select to install QuickTime 7 (it actually installs only the Player) from there.
If you don't have your Snow Leopard install disk handy, you can download QuickTime 7 Player for Snow Leopard here:
http://support.apple.com/kb/DL923
Regards.