Sebastian's answer is exactly what you need, as long as you don't mind the whole LabVIEW development environment starting up in order to run your VI (and staying open afterwards). Just put your VI, or a link to it, in the Startup programs group - I assume we're talking about Windows here, of course.
If you actually want to create a stand-alone .exe file that doesn't need the development environment installed on the PC where it runs and behaves just like any other .exe program, you need the Application Builder. I don't know if you'll be able to buy this for LV 5 any more, you might have to upgrade to the latest LV version - in which case ask NI for an upgrade price.
