Your description sounds weird. Forgive me if I misunderstood.
If you have four disks, created eight partitions on them, and then created a single RAID 5 over those eight partitions, then you have not understood the concept of RAID at all. You would have no redundancy in such a setup, and a single drive failure would be catastrophic. You'd be better off without RAID at all than use it in such a broken way.
If you have four disks, the number of devices in the array must be at most four (one for each disk). You must not use the same disk twice for the same array. (It's okay to have separate arrays for swap, data, etc, if the disks are partitioned accordingly).
The Desktop Live CD doesn't really support Software RAID. You can still do it; if you know how to set up RAID manually and create filesystems on it and (after the installer ends) chroot into the freshly installed system and make it bootable manually. But this requires in depth know how of all processes involved. And it may still fail, as the Destkop installer isn't supposed to be used this way and may fail to finish the installation properly.
It might be easier to just use the Server install, have it set up Software RAID for you, and then proceed to install the missing desktop environment packages once the "server" system boots.
Alternatively you could use the Alternate-CD to install Ubuntu. It's only available for Ubuntu 12.04 but nothing would stop you to upgrade to 13.04 after installing. You can find it here http://releases.ubuntu.com/precise/