You can't for movies; those will always be tied to the Apple ID under which they were purchased. Music is not copy protected so it can be shared, though the original Apple ID will be needed to re-download the tracks.
If this will be on a single computer, this should help for sharing tracks with another person:
iTunes: How to share music between different accounts on a single computer
Note that when it says "publicly accessible location", it needs to be a place where everyone has read and write access. The most common such place is the Shared folder in the Users folder, but you can place the music elsewhere if you change the access permissions manually (don't start tinkering with permissions unless you're confident you know what you're doing and can reverse things if they get messed up).
Regards.