In VirtualBox 4.0 disk size expansion is supported ------------------------------------------------------------------- 1) Run this command on the host machine, with due consideration to the actual paths applicable: d:\> vboxmanage modifyhd winXP.vdi -resize 25600 where, 25600 is the absolute final size desired ( not an incremental value) 2) Once this command has run successfully, invoke the virtual machine 3) Now, download/ install/ run the "EaseUS Partition Master" utility in the virtual machine 4) Create a partition from the unallocated disk space 5) Merge this partition to the main drive in virtual machine 6) Boot the virtual machine couple of times, as directed by the UI messages. That's it!