Sucker!!!!! (Ask me how I know...)
Get yourself a bunch of 2x4's and some carriage bolts, washers and wing nuts. Build the uprights like you would the corner in a house - two 2x4's with scraps of 2x4 between them. The scrap between creates a space that a perpendicular 2x4 will just slide into. Place the scrap so that the 2x4 that slide in sits on top of the scrap between the doubled up 2x4's. Run a carriage bolt through the intersection and throw the washer and wing nut on it. Don't go crazy trying to brace the thing seven ways to Sunday until you put it all together and see how rigid the assembly is. Even then, use minimum bracing. Remember - this is not a house, it's a game booth and it will see little use. Set up and knock down are as important as making something that will withstand the next 8.5 earthquake.
-Mike-