Assume that you want to create a partition in /dev/hda,
follow these steps and check if works:
1. fdisk /dev/hda and use the subsequent commands in fdisk, 'm' for help page
n => new partition
select primary and follow the instruction
p => print the partition table
l => to see the id for vfat, its 'b'
t=> to chage the id, and then enter 'b', the vfat id
w=> save the changes.
now make a vfat partions on the newly created /dev/hda1 partition
# mkfs.vfat /dev/hda1
hope it will help.