Ignore the advice from Adam Wolfe - it's nonsense. Use the Debian installer (advanced mode) to create the RAID 5 array on drives with just one partition (whole disk) as /dev/md0. Then partition the RAID 5 array into / and /home. Install and reboot.If you are using Wheezy this will work directly. If you are using Squeeze then you may need to fix the UUID in /boot/grub.cfg.I've done this successfully several times. It just works.
Eh. I tried that too. Grub failed to install.