Pete,

The string you are refering to is compiled inside a file called VsdWelcomeDlg.wid in your VS installation. You can change the default WelcomeText prompt using the VS IDE but this is not the same string and reads:-

"The installer will guide you through the steps required to install [ProductName] on your computer."

To change this prompt right click on your installation project and select View->User Interface from which you can get at a few properties per dialog.

Regards
Neil