If I put an exe into the startup folder does it open no matter what is the account you're logged in or is it account-tied?
In short, no. It's not the same. They usually are the same from machine to machine because most people use the default installation path. But the user can change that path. So you can never rely on it being the same. The entire thing is actually linked to reference in the registry for what path the system and user are installed on.
The method for determining that system path varies from language to language. You're going to have to look it up.
Also - it's a really bad practice to put an actual .EXE file in the startup. Make a shortcut for it.