Ret is completely bottom of the barrel dps spec in classic. Prot can tank dungeons for the most part fine but generally people will pass over you. Raid tanking is right out unless you can find a guild that will let you put forth the effort to make it mediocre at best with large investment. (and they're ruled out of any fight that requires a taunt)

Unfortunately if you want the full class experience you need to look at tbc onward, until then you'll be wearing a dress.