If you can login, you can click on the Apple in the menu bar>about this mac, and it should tell you the version of OSX you are running.
If it is 10.5.X Leopard (it will say on the install disk) follow the directions in this link.
Hope this helps,
Thank you for reply.
I did list the OS in my original question.
I had found the same advice on apple & followed the instructions & kept getting kernel errors.
I called apple support
They walked me through it again & still same error.
I took it into genius bar & they fixed in 15 minutes & still dont know why kernel error kept me from fixing it myself.