Raid1 post installation

Hello

They sent off a linux machine (installed with some software) to a customer.
Normally, when we install Linux (Cent OS 4.5) we do software Raid Level 1 during the
installation (/dev/sda and /dev/sdb).  This machine went out without them doing it.

The machine that went out should already  a /dev/sda and /dev/sdb (anyway to verify, if
/dev/sdb is not mounted?) and we need to perform Raid 1 on it, but we can't reinstall
Linux on it because it will overwrite evrything that is there.

Is there anyway to Raid a machine that already has linux installed on it without reinstalling
Linux over it?

Thanks