[CentOS] Please help! boot problem

Hi,

I have a setup with raid 1 and one drive has failed, and the other drive 
won't boot says missing os.

I thought I had it setup and tested but it would appear that it wasn't 
setup to boot form either drive.

How can I boot from the good drive that is missing the grub.

I am thinking of using linux rescue when booting from the centos 4.2 disc

This is a production machine and I don't want to mess it up.

Please help