Use any of the gui test tool. If cost is an issue, use the perl with guitest module. I've automated our installation procedure with it. Plus adding registry entry and file validation is really easy with perl.
I'd second that [in regards to Perl GUI test]. In addition, you should see if your installer can be run in Silent Install mode so that it can executed from the command prompt. Our overall installation process is a perl script that sets up specific registry entries and then executes the silent installer via system("start blah blah blah").
"What we elect to call imagination is mere combination of things not heretofore combined." - Frank Norris
What we elect to call imagination is mere combination of things not heretofore combined. - Frank Norris