I can see how to run a class file based on the instance of a symbol/object showing up on the stage, but is there to configure flash to run an actionscript file right when the program starts without creating any instances of a symbol/object first? If so, how do I configure it?
You can use a document class. It'll execute at the beginning of your application, effectively acting instead of timeline code. Depending on your application document classes can also be much more powerful and convenient than timeline code, since they aren't tied to specific frames and have a overall better format, especially if your application is almost entirely controlled by code.
An explanation and tutorial on using a document class can be found here.