hmm, unallocated would only show up if the section of HDD is not formatted at all. if they are seperate HDD's the contents of E: in the ubuntu istallation would most likely show up as:
/dev/sdc showing 110gb (NTFS)
if it is truly 'unallocated' then E: would show up as:
/dev/sdc1 50gb (NTFS) and
/dev/sdc2 60gb (unallocated)
picking sdc as the HDD to install from even if all of it is formatted as NTFS will bring up the option of allocating a portion of it to ubuntu (EXT) + linux swap filesystems
though you must choose to install alongside windows.
you can setup the partitions manually also
remember that /dev/sda is usually what windows would call C:
/dev/sdb would be D:
/dev/sdc would be E:
sda1 would mean first partition of C:
sda2 would mean second partition of C: etc..
though if its one HDD setup in partitionss then
c: = sda1
d: = sda2
e: = sda3 etc
hope this explains a little more, when i first installed ubuntu the unix way of identifing partiotions and HDD's was sort of confusing