* WARNING EXPERT USE ONLY *
If you right click on "My Computer" select "Manage" then "Storage" - "Disk Management" you should see your drive listed without a drive letter assigned to it, it will probably have a "Raw" or "Unknown" file system since Windows can't interpret the partition information. Make sure the drive recognised as the correct size.
PROCEEDING WITH EXTREME CARE so you dont loose any data from your other drives/partitions!!!
Right click on the drive and "Delete Partition", now you can create one or more partitions and once you format those partitions Windows will automatically assign drive letters to those partitions.
Hope this is the information you needed. Mentioning the version of Wondows you use would help to give a more precise answer as the menu wording varies between XP Vista and 7.