With fdisk:
fdisk /dev/hda [b](if your harddrive is IDE Master)[/b]
Bellow are the command for working with partitions.
Command action
a toggle a bootable flag
b edit bsd disklabel
c toggle the dos compatibility flag
d delete a partition
l list known partition types
m print this menu
n add a new partition
o create a new empty DOS partition table
p print the partition table
q quit without saving changes
s create a new empty Sun disklabel
t change a partition's system id
u change display/entry units
v verify the partition table
w write table to disk and exit
x extra functionality (experts only)
or use cfdisk which is more easier to create/delete/modify partitions
Regards
P.S. Anyway after that you need to format and mount