What I would suggest you do is this if you are trying to install Ubuntu onto the array:
1. Boot into live CD
2. "Try Ubuntu", don't go straight into the installer.
3. apt-get remove dmraid
4. apt-get install mdadm
5. Configure mdadm, and make sure that you take the output of "mdadm --details --scan" into mdadm.conf
6. Then assemble the array via "mdadm --assemble --scan".
7. Start the installer from the desktop.
8. Format from the installer and install to it.