Just a quick explaination. I assume that you are talking about one computer and several different people using that computer. The different between each person is two fold,
First there is a seperate file area under c:\document and settings for each user. So when the user looks at My Documents it is actually a sub-folder under their ID here.
There is a also a folder under each ID called Application data were programs such as Firefox and Outlook store user specific data.
Also under each ID are two folders called "Start Menu" and "Desktop" which is were user specific shortcuts are stored.
Note. This is also locked down by file permissions but as your users are all admins it does not matter.
There is special folder under here called "All Users". This is were common documents (called Shared Documents) are stored, plus common shortcuts for desktop and start menu.
The Second seperation is more critical and occurs in the registry. This is a special database that holds all the settings for your computer. The registry is split into an area which is system wide regardless of who logs on (e.g. hardware settings) and again a user specific area.
When an application installation, it normally puts it files into "c:\program files" and "c:\windows".
It also creates the short cut for the application. If the shortcut was created in the All Users desktop/start menu then anybody who signs onto the PC can see the shortcut. If the shortcut was created under a specific ID then only that ID can see the shortcut.
Enable to for all users to see a short cut created under a specific ID, all you need do is copy the shortcut from c:\documents and settings\<userid>\startmenu or desktop to c:\documents and settings\all users\startmenu or desktop.
When you run an application it finds out if the user specfic files and more likely registry settings already exist. It not then it will create a default set, thus any user can use the program.
Hopefully that all made sense.