I just saw Wilson and his wife's attorney, Christopher Wolf, on Hardball (Campbell Brown sitting it for the prissy one) and he (Wolf) said in no uncertain terms that Wilson did not become a supporter of nor start campaigning for Kerry until 2004. Your link clearly suggests he's mistaken or lieing.
Now it seems to me information like when Wilson became a Kerry supporter would be something a lawyer would get from his client so there's a distinct possibility that Joe lied to his own attorney.
Not necessarily an overly important fact but interesting nonetheless.