A disk drive can usually be formatted by right clicking on it in explorer. However, there are times when explorer is not available (windows pe, preinstall environment), and diskpart should be used.

 At a command prompt, type diskpart

Diskpart> list disk   ->lists available disks and their assinged numbers, you'll need this number for all operations on the disk

To format a disk, type the following commands on the DISKPART> prompt. Be careful to use the correct disk number, otherwise you may destroy important data. The following commands format the c: drive as a bootable primary partition.

diskpart
select disk 1
clean
create partition primary

select partition 1
active
format fs=ntfs
assign
exit

For more info, see. http://support.microsoft.com/kb/300415