It was mentioned here earlier that the Wii would be geting streaming support with Netflix. That system is now Live for use.
It works the same way as with the PS3 by using a software disk that stays in the system during movie viewing. No mention if there will be an update that will remove the disk requirement for the Wii, but it’s unlikely due to Wii’s limited storage space. Such a update for the PS3 is rumored for later this year.