Hello, The message is telling you to uninstall the current version of 'Dell support center', not windows installer.
I am using Windows Vista Home Premium SP1.  When I try to run a downloaded program (Dell Support Center application), I get a Windows Installer message "Another version of this product is already installed.  Installation of this version cannot continue.  To configure or remove the existing version of this product, use Add/Remove Programs on the Control Panel." There is no Add/Remove Programs on the Vista Control Panel.  The "Uninstall or change a program" window on the Control Panel does not include any version of Windows Installer. How can I install the new application?
Windows Installer Problem