rmmarsh: thats great I am glad you waded through all that text and found it helpful. :)
I do not know the specifics during the install wizards, as they vary from distro to distro and the install wizards may not support creation of a 3 way mirror (guis are generally limiting) but I can give you the theory.
You will want to use the manual or advanced partitioning wizard. (you might be able to pop into a virtual console and use the cli interface to do all your partitioning but I do not know exactly how to do that off the top of my head and I don't want to give you bad instructions.)
You should partition each drive identically, a partition for /boot (150MB is an accepted normal size), swap (typically 2X ram), and the rest for / (root, not the user root, the root of the directory structure). so you should have /dev/sda1,b1,c1 /dev/sda2,b2,c2 and /dev/sda3,b3,c3 all linux raid type.
Each of these should be set to the type linux raid or linux raid autodetect.
Once that is done there should be an option to create a raid, create a raid set choose mirroring as the type (raid 1) and select sda1,sdb1,sdc1 as the devices and for mount point set /boot, then do the same for sda2,sdb2,sdc2 and set it to swap, and finally for / do the same and select sda3,sdb3,sdc3.
If you have the option to install the boot loader (grub) on sda, sdb, and sdc do so. Again im not sure what the install wizard will present you with, it varies between distribution.
That should be all you have to do. After the system boots for the first time open a console and cat /proc/mdstat it should say syncing. Wait for that to complete. You can watch its progress with a command like "watch cat /proc/mdstat". It will re-run the command every 2 seconds and keep it in the window looking like a status window, a handy trick.
Once thats done you should experiment and ensure you can boot from any of the three drives. Its possible the installer will not install the bootloader (grub) on each block device, you can easily find out by changing your boot drive in the bios. Boot from each drive, no worries if some dont work, you can just switch back to the original boot drive that was selected during install time and boot up.
Report back and let us know your progress. if you get stuck some kind of screen shots or pictures of the screens your looking at will be helpful.
