Dual Boot Vista and XP with Vista already installed

Hi, I bought a new computer a few months ago that has Vista Home Premium on it. I am trying to instsall Xp in a dual boot mode. I have followed your instructions and created a partition. I now have 3 partitions "C" windows, "D" Recovery (was on computer when I got it), and the new one I created "E"
When I try to install XP the only drive that appears is "C" drive. Any suggestions on how I get the other drives to appear, so I can install XP?