What are the difficulties with adding a factory navigation system to an '02 A4 that does not have nav? Are the units sold on ebay really that straightforward to install ("plug and play")? Are any compatible with XM or ipod? I want a clean factory look with this capability. What about bluetooth?

Thanks.

That's what you should search for, here and on <a href="http://www.navplus.us">navplus.us</a>.