another hairy situation

i think my kitty has a hairball. he occasionally makes this horrible sound that's a cross between a dog's bark and a human's cough, and his body lurches like when he's puking up his just-inhaled-but-not-chewed-up canned food.

seeing as i'm a novice kitty-owner, and he's not my kitty to begin with, i'm a little on the overly-worried side. i don't think it warrants a vet trip (i hope not!), but perhaps a trip to the pet shop for some hairball helper? i seem to remember giving this sticky, molassas-type stuff to a long-haired cat we had when i was in Jr high. i dunno. i'm bordering on panickey, as i don't want anything bad to happen to lisa's cat!!!