I think the hardest part of that order to fill will be the auto anoucement..from a I assume the names in the system. Text to speech programs would have to be tied in and will probably be poor at pronoucing last names. Other than that part someone slightly more adept at programming than me could probably swing something like that without too much problem in something like visual basic. You could like perhaps run an overhead computer projector/DLP on a wall, have some sort of audio tone/alarm and flash the next group of peoples names on the screen in an attention getting fashion and display the count down timer or what have you.

I don't have your solution but I though I might offer a bit of input as to perhaps coaxing someone to program something for you.