I use DRIVE IMAGE 7 and the program only copies the part of the hard drive with data on it in your case 20Gb and you also have the option of compressing this data by up to 50% though it will take a little longer to carry out using this method.
DRIVE IMAGE 7 has been invaluable to me as I had that sasser worm recently so I just restored the backup and of course downloaded the latest Microsoft security patches to prevent it happening again!
CurlyWhirlwind
May 2004