SQL error…Help please

Hi there, very recently I downloaded and installed the Oralce 8i Personal edition on my PC.
At SQLPLUS prompt, I encountered the following error message. Could any one help me to resolve this?

select eno,enam,salary,dense_rank() over (partition by dept order by salary) from myp_employee
*
ERROR at line 1:
ORA-00439: feature not enabled: OLAP Window Functions

Thanks.