Does not assign a drive letter For Hard Disk

I just recently bought a new Hitachi 2.5 HDD with casing. When I plug it into my computer running Winxp Home it Identifies that a USB Mass Storage is there but does not assign a drive letter so i cant do anything . How to use this hard disk.

I also tried with Win 98 but it does not assign a drive letter
I also installed drivers came with it.

I can see the name of Hard disk in Screen coming when u see Attached hard disk and CD/DVD Drives.