First update your firmware to latest levels (if you haven't already).
IBM Entry Level Disk Storage: Overview - IBM System Storage
You'll need to install the SMclient software on a machine connected to the array. Often times this is a machine connected out-of-band directly to the ethernet mgmt port of the storage array... but I believe the software can send messages via the fibre HBA (in some cases) to communicate with the unit. You'll have to look at the compatibility matrix from IBM to determine if you have the right pieces for that... so I recommend that you do the out-of-band option.
Read all about it from the Redbook at:
IBM Redbooks | IBM System Storage DS3000: Introduction and Implementation Guide
I might have access to one of these devices at the office, but it's likely we've got it configured with some other kind of proprietary IBM sw... (let's just say IBM doesn't get a "user friendly" award in this case).
Anyway, assuming you can get a Windows or Linux host connected to the out-of-band ethernet port of the DS3000 and get the Storage Manger sw installed (SMclient), then from that interface you can configure LUNs, etc.
HTH,
Chris