I don't believe that the pre 2006 Rav4's have any way to connect an Aux audio input.
I installed one of the Scion headunits in my 2005 that offered the iPod interface.
They are a plug & play installation.
If you only want a Aux input, the T1807 would be your best bet.
If you want the iPod interface (control of the iPod from the headunit) there are the T1806, T1808 and T1809 units.
These are readily available on
ebay, and all offer a greatly improved sound output.
If I can help you any more, contact me at
rctech@comcast.net