Unallocated Disks

Hi

Hoping someone can help with this, we have a Clariion AX4-5 array,  this has 4 disks which are being presented to 2 hosts running win 2003 and win 2008 server, from Navisphere everything looks ok, the disks are all visible and online, the problem is from the Windows Servers under disk management the disks are showing but are showing as Unallocated. Previoulsy they had been setup each with a different drive letter and would then be accessed from My Computer using the drive letter. I cannot find a way of allocating each one of these disks a drive letter. I need to be able to map each LUN with a different drive letter so it is then presented to the servers. Is there something obvious i am missing? any help would be appreciated.

Just to expand on this i cannot reformat the disks from Windows because the disks have data on that i want to keep, previously the disks where used in a cluster on an old domain, we now have a new domain and i want to make the disks visible.

Thanks