Damn, saw this one too late. I guess there'll be another one soon, at least I hope so. For crying out loud, schedule this one for Sunday afternoon; I haven't had a Saturday off for weeks. When I drove down to the Air Force base last weekend everybody had gone home, except for a couple pro-slaughter assholes at the corner of Dale Mabry and Interbay carrying handwritten posterboard signs reading "support the troops!" (I do, those guys aren't children's playthings you know) and "Saddam is a smoking gun" (really! what the Hell is that supposed to mean?).
Find a surveying or civil engineering company. They all own large-format (typically up to 36" x 64"!) inkjet plotters for producing full-page engineering plans. Think of all the words and pictures you could put on a 3' x 5' poster! Most of these plotters even do color. The color plots don't last, but they look fine for a while.
Your best bet is to find a sympathetic CAD draftsman who works late; then you can get a few for free. Talk him into coming to the demo with you! Next best is any blueprint shop, you'll find one in any small city. I use Photoshop LE which came with my scanner, but practically every graphics program I've used lets you print blown-up bitmaps to large pages.
Yours WDK - WKiernan at concentric.net