Stereo upgrade- 2002 (9n) Polo E

My Polo's stereo is good, but I'd like rear speakers. It sounds like all the sound is coming from the dash which is a bit naff. There are speaker grills in the rear doors (it's a 5 door) and I'm going to have the inner panels off to fit central locking soon so would the built in stereo be able to have the rear added? The front stuff is actually quite good when I'm only listening to an iPod through an iTrip. It's got a Beta stereo (IE Tape deck and radio only), does this have the right connectors (it's not got the forward/rear fade button like the one in mum's Caravellle) and the power to drive extra speakers? Also, where best to get suitable speakers? I don't know what are normally put in the Polo, but a similar wattage and size is probably best.
Thanks,
Felix

You will need to get a gamma radio or any good headunit for rear speakers, you will probably have to run speaker wires to the rear doors also, as I don't think the E model will have the required wiring fitted as standard.