While I've never designed a convention booth set-up, I could certainly help you out with any signage, brochures or flyers you may want to distribute as part of your display.

What I do as a desktop publisher is produce just about anything you can think of that's typed (or, to be more precise, typeset) on my Mac - brochures, newsletters, letterhead and business cards, resumes, garage sale flyers, wedding shower invites, etc. I could also design signs which could be enlarged on a poster-size photocopier or at a printer's, depending on how professional you want it to look and how expensive you want it to be.

I'm sure we'll have spoken with each other by the time you read this!