Hello again, and thanks very much for your additional information.
What you're describing are tapeworms. These are gotten by ingesting an infected flea during self-grooming, so your cat will also need to be treated with a monthly flea preventative.http://www.sniksnak.com/cathealth/tapeworms.html
For the tapeworms, a de-worming medication from the vet, would do the best job. If you've already tried an over the counter wormer and were not successful, it's usually not strong enough. If the wormer contains the active ingredient PRAZIQUANTEL, this is what will get rid of the tapeworms. The flea treatments you should consider, are Advantage, Frontline or Revolution, sold by your vet or bought online, at a discounted price. The over the counter flea treatments are not effective, nor safe. Many cats (and dogs) have experienced very dangerous side effects (some even fatal!) after being given other flea treatments, like HARTZ, SERGEANT'S AND ZODIAC, so just make sure to only use a flea treatment sold by your vet.
Usually, wormers need to be repeated in 2-3 weeks, to be effective, so follow directions on the package, and/or follow up with what the vet tells you.
I hope this problem is resolved for your cat, very soon!