no worries that narrows it down
very simialr system to the 2002-2005 IS200/300 systems
try another CD (where is map cd) that can be found on the later model 2nd gen IS and 3rd gen GS
if that fails then it could be the Map CD reader in the boot or give it a good clean with a cd cleaner
i have replaced a few on the 1st gen IS in the past few months and that seemed to work