How to install QuickTime 7 without overwriting the currently installed version
The QuickTime Player 7 and QuickTime 10 apps coexist on all my Macs without causing any problems.

If you're worried about overwriting QuickTime Player 10, right-click on the app, and choose Compress "QuickTime Player.app" and zip it up. If the QuickTime Player 7 installation wipes out v.10, (and I don't think it will,) then you can simply uncompress it.

You can also retrieve it from a Time Machine backup. You do use Time Machine, don't you?