Hi Prastie
you mean that the win 7 partition is detected in Disk Utility and the Unpartitioned (unallocated ??) is not ?
if you can see win 7 partition, you can simply format Unpartitioned part in win7 to NTFS
after that if for some reason Disk Utility detected your partition but is unable to format it as Os Extended (Journaled) [it happens]
you can use [Paragon Hard Disk Manager™] in win 7 and format it as Apple HFS.
Hope that helps.