disk druid offers you this option. first, you need to create two similar partition (one in each drive) for a partition mount point (i.e /home or /usr). forex, to create /home:
1. create a partition in /dev/hda and then /dev/hdb with similar size:
/dev/hda2 - 10 GB
/dev/hdb2 - 10 GB
the filesystems should be set as "Software Raid".
2. once the partitions are created, you can then select the option "Make RAID" in druid's main menu. here, you'll be asked which pair to use and what mount point will it be assigned to.
once the raid partitions are created, disk druid should show it - /dev/md1 with the corresponding partitions (/dev/hda2 /dev/hdb2) linked together.
the gui installation is a straight forward process so i'm sure you won't get lost there.