Are you trying to install Ubuntu alongside Windows 7 or Windows 8 but can’t see your disk drives in the installer?
You might still be able to see them in the Disks tool but not the installer.
A quick fix that worked for me was to remove dmraid:
sudo apt-get remove dmraid
Then run the installer again and presto! your disks are appearing again.
I did this using the live cd but from the text installer you can perform the apt-get command in a shell by hitting Shift-F1 to get to a shell then “sudo apt-get remove dmraid” before you get to the disk part of the install. Or go back in the install process and retry that step after the removal of dmraid.
Let me know if this helped you out any, it was handy to find this out myself.
-Pete