If you want to open package files on the install disk to install any apps, download the free Pacifist from version.com or macupdate.com, among other sites.
You need to use Pacifist because it installs all the app files to the proper places on the Mac.
To open packages on your Mac, right-click the file and choose Show Package Contents.
My install disk might be different from yours because mine is going on five years old. After clicking the arrow at the bottom right one screen past the licensing info, there's an Options button at the bottom that when clicked shows the Archive and Install option.
You have to put the DVD in the machine, then restart it while holding down the C key, so it will will start up from the DVD.
(You have to hold down C rather than D because Apple's installers were on CDs before DVDs came along.)