CentOS - Dec 2009 - moving from live partitions to raid1 on an eserver

I have a qtp (qmail toaster plus) machine on an ibm 326 eserver that has 
2 sata 250GB drives.
 The problem I have is that when the Os was installed I thought I had 
hardware raid on but to my avail the Os assumed to drives an installed 
accordingly. Here is what df has for the partitions.
# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sdb1            240362656  17843040 210309816   8% /
/dev/sda1               101086     11843     84024  13% /boot
none                   2047316         0   2047316   0% /dev/shm

I need a raid in place on this machine. This is a live machine but I do 
have a lab machine to break.

I really need to move this in a live fashion without losing the data of 
course I have complete backups to start a new if need be but it would be 
nice to be able to make the change and have raid1 in place to have a 
some better redundancy.
 I guess what I am asking what are the basic steps and what warnings to 
look for?
Thanks
--Dave