admin privileges

I am posting this on behalf of a friend of mine who has XP
but is not computer savvy who has XP set up by his son (an
expert)who now lives in San Fran .

I am an experienced Windows 98 user.

This is the problem.

My friend has 1 admin and 4 users.(His family)

He wants to be able to load software that can be used by
all the users. Currently digital editing software.

When I tried to load Adobe Photoshop for him yesterday I
got an error message saying roughly "You do not have admin
privileges".

I am the administrator and I have the password, but I want
to know how can I install ALL his software so that it can
be used by all of the users including the admin (me).

I find this aspect of XP very confusing and frustrating.

Please help me if you can.

Edward