I just googled and found this site that seems pretty good. Don't panic. But see your vet asap:
http://www.buzzle.com/editorials/6-1-2006-97997.asp
There's much more on the site, but the spaghetti-like description sounds like roundworms.
ROUNDWORMS (Toxocara canis, Toxascaris leonina)
There are two types of Roundworm: Toxocara canis and Toxascaris leonine. This is the most common type of dog worm, which affects the intestines and causes a pot-bellied appearance, mostly in puppies. There are a few ways puppies can become infected. Puppies are often infected before birth through the mother’s uterus or through her milk. Puppies can also contract these worms through the ingestion of an infected animal (such as a rodent) or infected soil. Roundworm eggs can live in soil for many years. Once a puppy has ingested the infected soil, the eggs will hatch in his intestines, allowing the worms to live there and grow to adulthood. These adults will then produce more eggs.
Roundworms may be found in your dog’s stool or vomit. They can grow to about 7 inches in length and have a spaghetti-like appearance. If this type of infestation is not detected early and is allowed a chance to develop, a buildup of worms in the intestines can cause an obstruction which may result in death. The symptoms of a severe infestation are: pot-belly appearance, diarrhea, vomiting, dull coat and weight loss.
Puppies should be dewormed every 2 weeks between 2 and 12 weeks of age, then monthly until he is 6 months old. Once your puppy has reached 6 months of age, he is less susceptible to contracting these worms but should continue yearly exams (or more often if considered high-risk).
Because Roundworm can be transmitted to humans, it is important to promote good hygiene, such as washing your hands regularly. Transmission of this dog worm to humans is usually through infected soil, which may be in your backyard or front lawn. Because the eggs are sticky and can easily adhere to hands or clothing, make sure children (and adults) wash their hands after playing outside (especially at a park or playground), after playing with the dog and before it’s time to eat.
Treatment generally involves administering oral medication (dewormer) with follow-up fecal exams and a monthly heartworm medication. Try 1-800-PetMeds - America's Pet Health Resource
Prevent your dog from contracting roundworms by cleaning up fecal matter from the backyard as often as possible. Also, administering a heartworm medication such as HeartGard - Prescription Heartworm medication for Dogs & Cats is a good preventive. Do not mix wormers and consult your vet before giving your dog any medication. And last, but not least, always remember annual exams.