DrT,
Heath was originally voiced by Tyler Bunch for the first season and then Peter Linz in season 2. I think. I have to check on that. The rest of the cast is as follows....
Peter Linz: Theo (saseons 1&2), Heath (?Season 2)
Jennifer Barnhart: Cleo
Kathy Mullen: Leona (seasons 1&2), Infomation Hen
Pam Arciero: Leona (season 3)
Anthony Asbury: Lionel
Heather Asch: Click the Mouse, Clay Pigeon, Marmy Smartypants
tyler Buunch: Clay pigeon (season 1), Heath (Season 1)
Jim Kroupa: Clay pigeon (seasons 2&3)
Tim Lagasse: Theo (season 3) Buster, Arty SmartyPants, Gus the Bunny
Jim "Nappy" Napalitano: Mr. Webster, Sgt. Exclamation (for the vowel boot camp bits.
Some cameos....Anthony Asbury appears as himself in the Shakepeare episode. And Tim can be found in the background of "Red Hat, Green Hat" in the lower right hand corner of the screen. He's sitting at a desk with a monkey which he's also puppeteering. tim also built the puppets for that story as well as the 3 dimensional puppets for "Daedalus and Icarus". jim Napalitano did the shadow puppets for that piece. Also look for Jim and Tim in the epsiode with the Sicialian Marionette troop. That's jiim and Tim up on marionette bridge with Sal.
--Matt