Is it possible to install software RAID on the below o/s & config?
Core 2 Duo 2GB Memory Dual 160GB SATA II Drives Centos 5x 64bit
Please explain how,
Yes, it is possible. Software RAID on Linux can be set up as long as you have multiple devices that Linux can see.
You have two Drives? Do you want RAID1?
By far, the easiest/best way to do this is during the installation process; it's fairly straightforward at that point. I'd suggest setting up a small software RAID1 for /boot and the rest of the drives allocated to a software RAID1 under LVM. There's screenshots and whatnot in the docs walking through the process here: http://www.centos.org/docs/5/html/Deployment%5FGuide-en-US/s1-raid-config.html
It's possible to do after the fact, but needs more details (what your actual partitioning is, whether you're using LVM or not, etc) and is fairly involved.