Mac OS X 10.5 Help
If you can’t move an application
When you set up your computer for multiple users, you can designate whether users have administrative privileges, meaning they can control certain settings and perform certain actions on the computer, such as installing applications.
If you log in as a user who isn’t an administrator, you don’t have privileges to change the Applications folder. In this case, when you drag an application from the folder, the Finder makes a copy of it.
To move applications from the Applications folder:
Log in as an administrator user.
You can move applications you have installed in your home folder.
To make an application easier to locate, you can create an alias for it and keep the alias in a folder or on your desktop.
You can also add applications to the Dock to access them quickly.