SCStan

My Wife's 02 ES300 with a little over 100k miles has started having Navigation system problems. The navigator is giving out different symptoms at different times but it's stuff like I cannot get it to accept our home address any more, or it quits talking at times. Anyway, Where do I start with this thing (other than the Lexus Dealer)? Is there a system re-boot, or maybe a new disk I should be looking at? If anyone has experienced problems with their Nav system, I'd like to hear about how you got it squared away. Thanks in advance!
SCStan