The actual size of the drive should be 156.25gb.
You get this by 160/1024=0.15625*1000
It won't let you because fdisk was done away with in WindowsXP. The command you want to use is format.and they were all command line using fdisk. I tried doing this in a command prompt and it wouldn't let me.
Partition it into sperate 32gb sections. If you don't windows will read a disk error and run chkdsk.