They are starting to charge tax in most states because the states got wise to that. The days of tax free online purchases are coming to an end.
For both Netflix and Amazon, you will need to log in on the PS3 and a PC. Choose "register device" on the PS3 from each of the applications (you will need to install them) and login to your account on those services on your PC and they will provide you with a code to enter into the PS3 application and that should be it. Almost sounds a little complicated, but they provide you with all the instructions and it is pretty easy.