Navigation software update?

[blakesr]

I am in the middle of purchasing a 2002 X5 (which everyone on the board has been so helpful with) and it has navigation. I have a coulple (more) questions regarding it:

What is the difference between a software update for the nav and a map update?

I have 5,000 miles left on the original warranty, does this warranty cover the software update? Should the dealership do this update for me?

For the MKIII unit, what features does the latest software upate have?

Also, if I decide to have the dealer upgrade me to a MKIV nav set up with Sirius, what do you guys feel is a fair price?

Any help is appreciated!