euanaj,
If you're using ESXi's software initiator, it will only connect with a single iSCSI target. Because of the way the iSCSI Terastation works (additional volumes are addressed through another iSCSI target), this will only allow you to set up storage on a single volume. The IQN address of the targets are unique, they show up as something like "iqn.2004-08.jp.buffalo:TS-RIGLBDF-001D73267BDF:volume1". After the reversed domain name, the IQN includes the device's hostname as well as the MAC address, so they're certainly unique.
Everyone,
We've never claimed that the iSCSI Terastation is compatible with VMware's products. I've personally seen it work fine with ESX version 4.0, but only in a simple setup with the ESX host connecting to a single volume on the Terastation. It does work fine with the Microsoft iSCSI initiator, because that software initiator can handle multiple targets.
I'll forward a feature request to have this looked at, but I can't promise anything.