InfoPath Dev

I need a bit of help please.  I have a form created where I have a submit button.  I'd like to make the submit button active ONLY when a certain user opens/edits the form.  The user's name is generated into a textbox on the form via Get Users Info web service.  What I can't figure out how to do is create the rule that says only if "this user" (the name from the box) equals the logged on user does the submit button become active.

doable?

Set conditional formatting on the submit button

if username_textbox is not equal to username()

hide/disable the button.

Thanks!