You mentioned a 500GB drive in your initial post, but the output shows a 300GB drive!? Can you confirm it's the 300GB drive which should contain the VMFS datastore?
Did you setup the host with ESXi 4.0 or was it upgraded from an earlier version (which one)? If it was upgraded from e.g. v3.5 it might be sufficient to just need to change the partition type from 83 (Linux) to FB (VMFS)? However that's just a guess.
André