Did you purchase it? Partitioning comes with EE (enterprise edition) as an option on top of enterprise edition, not with SE (standard edition) or XE (express edition).
Edited by: Solomon Yakobson on Jul 13, 2010 9:21 AM
This is a bit late for the original poster, but maybe by adding it here it will of use to someone else in the future.
There are many database options that are linked in with the oracle kernel when it is installed.
This happens by default when you pick the Enterprise Edition.
If you choose not to install them you cannot just add them with dbca, you must re-link the kernel.
These were the instructions I got for adding in the partitioning option.
$ cd $ORACLE_HOME/rdbms/lib
$ make -f ins_rdbms.mk part_on
$ make -f ins_rdbms.mk ioracle
10 out of 10 for this rrp.
I was installing Oracle 11g Grid Control, and got the (apparently not uncommon) prompt that partitioning was not installed. I ran your 'make' commands, and looks fine now, resulting in me not having to uninstall / re-install.