Get some information on the VMDK you are going to convert

VBoxManage showhdinfo Windows\ XP\ Professional\ 2.vmdk

VBoxManage showhdinfo Windows\ XP\ Professional\ 2.vmdk
UUID: 880b32c8-db80-4caf-94d4-f7af29b691d3
Accessible: yes
Logical size: 10240 MBytes
Current size on disk: 10240 MBytes
Type: normal (base)
Storage format: VMDK
Format variant: fixed split2G
In use by VMs: Windows XP Pro 10GB (UUID: 66041cc2-a2c6-4e92-bd9d-ccdc0f166f5c)
Location: /mnt/2TB_VOL2/Virtual Machines/Windows XP Pro 10GB/Windows XP Professional 2.vmdk

Using VBoxManage convert the VMDK to a VDI image.

VBoxManage clonehd Windows\ XP\ Professional\ 2.vmdk winxppro10gb.vdi --format VDI
# note I made the mistake of naming my VMWare vmdk file with spaces which makes it harder to run command line programs
# Don't give your VM's spaces in their names!

Enlarge the VDI file

VBoxManage modifyhd winxppro10gb.vdi --resize 40960
# resize virtual hard drive

Mount the VDI file in a GNU/Linux VM and delete and resize the partition

I next used a Fedora 17 live ISO and created a Virtualbox VM, added the resized vdi file to it as secondary hard drive and booted from the live CD into Fedora 17.

Then get root in F17 and

fdisk -l
# list your fixed disks and make note of the start sectors
fdisk /dev/sdb

# delete the partition
# I ran into a problem here the start sector was 63 and
# F17 fdisk wouldn't allow me to recreate the partition at a start of 63 only 2048
# restarted using the -c option and I was allow to create a start of 63
fdisk -c=dos /dev/sdb

# remember once you have 'd' deleted and recreated 'n' the larger partition
# you need to mark it as active 'a' and label it 't' as NTFS (7).

# write 'w' the new partition to disk.

# run ntfresize
ntfsresize /dev/sdb1

# by default this expands the ntfs to the full size of the partition

# so you don't need other options other than the partition device name