Not entirely clear from Info Center, but POWER5 and POWER6 processors appear to require HMC. Older systems can use Navigator. (But I thought, somewhere along the line, that the size of the system also mattered, as in small systems could use Navigator but big systems needed HMC.)
We have a POWER 7 box and so far I'm hearing that the old DST-style partitioning was only to create 1 extra Linux partition. As of now, you need an HMC or SDMC to do partitioning. So there goes another $10k.
I believe that on Power 6 you can do it if you've configured an ASMI terminal, even if you don't have an HMC. We are in that situation, though we are only using a single partition at the moment.