i was at an office this morning trying to remove the anti virus and install avg and security essentials as well as installing SP3. three of the six machines worked fine but the other three came up with the error message you do not have permission to install this software even when run as administrator.
does anyone know what this is and how i can get round this?

To set user permissions in Windows XP, you need to reboot in Safe Mode.To do this, click on Start.Then click on Run.The Run window will appear.In the textbox in the Run window type in the following: Msconfig Then press Enter or click on OK.The Msconfig window will appear.It allows you
to configure how your computer runs.Click on the General tab in the Msconfig
window if it is not already selected.Under “Startup Selection” click on the
little circle next to “Diagnostic Startup.”A little green dot will appear in the
circle next to “Diagnostic Startup.”Click on Apply.Then click on OK.
Now your computer is set to startup in Diagnostic Mode, also known as Safe Mode.
Click on Start.Then click on Turn Off Computer.Then click on Restart.When
your computer restarts, it will restart in Safe Mode, instead of restarting
normally.Safe Mode will look different then Normal Mode in several ways.The
cool looking blue and green Windows XP Startbar will be replaced by an old
fashioned grey startbar.Your custom desktop background image will be replaced by
a boring single color.And windows may appear really large since Safe Mode
operates in low resolution.Don’t worry; your computer will be back to normal
once you restart in Normal Mode.
So, if a login screen appears when Safe Mode loads, click on any account with
Administrative rights.In some version of Windows XP, only accounts with
administrative rights will be listed in the Safe Mode login screen.Once logged
in, double click on My Computer or right click on Start and then left click on
Explore to access Windows Explorer.Then go to whatever file or folder you want
to set user permissions for.Then left click on Properties.The Properties
window will appear.In the Properties window, click on the Security tab.You’ll
see a list of the user accounts on your computer, and underneath those user
accounts you’ll see a list of user permissions.First click on a user account
that you want to set permissions for.Look at the list of permissions.Next to
each permission are boxes under the Allow Column and under the Deny Column.If
there’s a check mark in a box under the Allow Column, then the permission listed
to the left of the box is allowed.If there’s a check mark in a box under the

i think if any anti virus run before remove it and also from registry some time some file stored here than your installation may be successful