Never played Starcraft 1, but isn't Starcraft 2 and Toy Story totally diffferernt? so why have a crossover :/
Zerg have always been there since SC1. And yes, different spelling. FUN FACT: Before SC1 was released, they were spelled "Zurg." 0:36 [youtube]j4G566MKLEE[/youtube]
And Zerg does not = Zerb. Here are some Zerb warriors from the cartoon Earthworm Jim. I had to use a screenshot cause I could not find a pic of them online.
http://www.lemonamiga.com/games/details.php?id=3518 Zerg in 1989. It's a little rpg set in the land of Aiur. There are Goblins and Trolls and other nasty things hindering your quest to defeat the Zerg. Once the overmind is killed, Aiur is freed and you are victorious.