recover a failed mirror and boot partition when primary hdd fails

I have a server with Raid 1 mirror – Server 2003 Software raid
My primary sata hdd has failed. I am trying to boot off the secondary so I can install the new hdd and recreate the software raid 1
When I boot the machine off the slave it takes me into Server setup and says it cannot locate the files needed, please install the server 2003 disk.

I managed to recreate the raid before when I edited the boot.ini but cannot remember what I did.
How can I boot off the slave and recreate the mirror???