Drive images - filling free space with zeros

So, one of the things I've been doing is drive imaging. I've got 3 systems that are to be identical (based on, of all things Freedos...) So, I thought it was a perfect opportunity to dust off cloning/imaging software. So, I've been using the excellent g4l (ghost4linux) which is now up to v 0.22 (I make use of this for trying to rescue failing hard drives too as it includes dd_rescue). Anyway, the new machines have 80GB drives and the lzo compressed images are running ~450MB.... but one of my questions was making sure that it was as small an image as could be. I found that there are a few ways to squish the image file more and that it mostly revolves around filling the empty drive space with zeros.

Here's a mirror of ftp://fedoragcc.dyndns.org which has a number of tools, including blank6.exe for dos (which creates empty 2gb files until the disk is full, then deletes them.) There's also cleandrive which does the same thing for a dos/linux system (basically dd with /dev/zero as the input file and /dummyfile as the destination, it fills, runs out of disk space and then it deletes /dummyfile. Really simple concept but it could squeeze out some space.

On a fresh install to a brand new hard drive it was more trouble than it was worth, but I can see how a "lived in" install would certainly benefit. (I should mention that this would be a decent way to make it harder to recover deleted files - certainly not as secure as filling the space with a random hash, and rehashing, but... don't do this if you've just deleted a file and hope to recover easily.)