"i am using redhat linux9. i have 15GB disk space mounted as a /dev/hda1 outof 20GB harddisk. i need to add the rest of 5GB free space to the existing partition or create a new partion. please help me in this matter."
I would advise you to create a new partition using fdisk and use all of your free space in the new partition. Then you can copy part of your system to the new partition and mount the new partition using /etc/fstab. Here is a thread that contains an explanation of how to copy /usr to a new partition.
Be prepared. Create a LifeBoat CD.