The vditool executable above only works on 32 bit systems. If you have a 64bit system then use the "vditool" image and library path from your existing VirtualBox ... nstallation. The following commands suit an AMD64 system running Ubuntu 7.10:
<code>
LD_LIBRARY_PATH=/usr... itool SHRINK new-file.vdi
</code>
(These commands should actually work on both 32bit and 64bit systems).