In redhat9 you can also use parted, if you are wanting to partition a disk that is currently in use make sure to either boot into rescue mode or unmount any partitions on the device and turn off your swap.
example:
parted /dev/hda, 'print' to make sure you have enough space on that device. You can have upto 4 primary partitions with no extended partition on a device. If you need more than four partitions you can have 3 primary one extended and multiple logical within the extended.
To create a primary with an ext3 file system 'mkpart primary ext3' The changes take place as soon as you hit enter so double check all of your commands.
I'd recommend downloading or bookmarking all the Howto's from redhat's site
http://www.redhat.com/support/resources/howto/rhl9.html