Update on my betta:
THANK YOU, THANK YOU, THANK YOU! My betta's doing a HECK of a lot better now that he has a nice plant to play around (re: hide in) and some good pellet food. I think he's just really young and unfamiliar with the domestic life. His fin is beginning to unclamp and he's generally more playful -- he won't stop wiggling (he loves it when I wave to him for some reason ...)!
Anyways, thanks again! :D