Adding a new SQLServer instance..where's the install files?

Greetings to the well of knowledge...

I need to add a new instance to an existing SQLServer installation.  The process seems straightforward enough but I'm at a road block.

As everyone knows, one needs the SQLServer install media in order to add the instances.  Problem is the install media I have is a single executable file.  I have tried running the executable and it produces a temporary folder of files that look like it could be install media.  However when I am prompted to provide the location of the install media, it saiys that that this is not a valid install medium.

Help?

Thanks,

Ken