Are they Canadian or American tylenol 2s?
Canadian ones are: 15mg codeine, 15mg caffeine, 300mg acetaminophen.
American ones are 15mg codeine and 300mg acetaminophen.
In the case of the American ones, eat all 6 for 90mg of codeine. Otherwise save them for headaches - 90mg caffeine will far overpower the codeine.
In the worst case (some sort of generics with 350mg apap) you will only take a little over 2 grams of APAP, which is fine but may upset your stomach. Some people would suggest doing a cold water extraction (search around) but for 6 tylenol 2's, it's not worth it, IMO.
90mg codeine is very weak but it should provide an OK high if you don't do other narcotics with a regularity (e.g. percocet/Oxycontin/oxycodone or Vicodin/Norco/hydrocodone).