The NVL2 has appeared in the 9i documentation, but interestingly you can get this function in virtually any 8.x version of Oracle. NVL2 is an extension of NVL, being

NVL2(a,b,c) = if 'a' is not null then return 'b' else return 'c'

and you'll probably find its available in your current release...
SQL> select nvl2(1,2,3) from dual;


SQL> select * from v$version;

Oracle8 Enterprise Edition Release - Production
PL/SQL Release - Production
CORE Version - Production
TNS for Solaris: Version - Production
NLSRTL Version - Production