Hi, just googled it and came up with http://www.centos.org/docs/5/html/Deployment_Guide-en-US/s1-system-config-lvm.html - useful?

Thanks,
Neil

First you have to create a partition with fdsk /dev/sdX (where X is the letter of your each drive).
Then if you have LVM follow the LVM howto (http://tldp.org/HOWTO/LVM-HOWTO/).
If not you have to make a new filesystem and mount in a new mount point.

Or you can simply use Gparted from a live Linux distro.

See also
http://www.linuxforums.org/forum/suse-linux-help/83611-how-extend-existing-ext3-paritiion.html
http://www.linuxquestions.org/questions/linux-hardware-18/how-do-i-extend-an-ext3-partition-408599/

Andre