RunApp Q for Anthony

Hi Anthony, Having a problem with opening files using RunApp. Opening the .exe file is fine. But what I am trying to do is have a control button open the attachment file that is shown on a form using an 'onclick' event.
I have tried to use the DLookUp alongside the exe. file path when filling out the command line in macro builder but to no avail.
How do you specify that the file opened should be the one showing and no other. Also, and I'm pretty sure this is why it's not working, but how precisely do I write it out. Am I writing it in SQL or VB or something else. The finer points of using square brackets and paretheses still evades me.
Cheers
Tim