Creating Software RAID arrays on Debian systems:

apt-get install mdadm
fdisk and create partitions type 0xfd
mdadm --zero-superblock /dev/hda /dev/hdc
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd["ac"]1
mkfs.ext3 /dev/md0 

Add entry to fstab:

/dev/md0 /home ext3 noatime,rw 0 0

Create mdadm config file:

panther:~# cat /etc/mdadm/mdadm.conf
ARRAY /dev/md0 devices=/dev/hda1,/dev/hdc1 level=1 num-devices=2 auto=yes
DEVICE /dev/hda1 /dev/hdc1

Note that the array is actually started in /etc/rc0.d/S50mdadm (via mdadm -A -s) or mdrun command