Have a look at the TABAR in zombies '09, it has airburst. as for exploding x pixels into a substance, you'd more likely just have a normal airburst switch that activated a timer before executing the airburst function rather than executing it right away.
My code's probably ugly as hell in retrospect, post any bits you don't understand (preferably on
pastebin) and me or someone else will give you a hand.