Hi zzjones, I have a 2003 SC430 as well with version 2.1 nav disk. Our year has a "Generation 2/3" model of the dvd/navigation player. I am pretty sure generation 4 or 5 will not work in our model year. When looking for an updated disc, make sure it is a generation 2/3 disc. You will see alot of used disks on Ebay or possibly Sewell Lexus in Texas usually sells the older version of nav disks for alot less then the newest 10.1 version. http://lexus.sewellparts.com/closeout.html
I have never ejected my disk yet, but thankfully it is easy to get to in the trunk. If you find an updated disk, it is just like installing software on a computer, eject the old disc and input the new one and the system installs the new software.