The compatibilty mode is generally set after the installation by right clicking on the desktop shortcut and selecting the third tab(compatibility) and checking the first item in order to drop the menu of choices(95, 98/ME, NT with Service Pack 5, and 2000). The problem here is getting the installer to run on XP. If the compatibilty tool allows the installer to run then setting the compatibility mode with a right click on the shortcut afterwards or creating a shortcut in order to set the mode would allow you to run it. The help+support instructions there only refer to the Start menu which would work if the installer creates a link there in the program group. Some older programs only create a desktop icon to click on. What type of program are you trying to install there?