Well first off, if your going to be playing DVD's, there really is no need to create a /mnt/dvd. You should just be able to use the existing /dev/dvd as your device to play from. Usually when creating a /mnt/dvd.. etc, its creating an empty directory so you can mount and view data cd's or dvd's. Media like CD's and DVD's you cannot mount.
But if you really need to know how to create a link, it would go like this:
ln -s [source] [destination]
So you could do something like this:
ln -s /dev/dvd /mnt/dvd
And about installing those packages, don't use the browser, install from the command line. What type of files are they, source or RPM ??