If I do a fresh install of XP and then run Eraser 6 (from Source Forge) to overwrite all the free space on the drive won't clonezilla write every bit of info from the cloned image to the new hard drive so I don't have to run DBAN or another utility on every drive?This could save a lot of time, dban takes quite a while to run and Clonezilla can write a 40 gig drive on these machines in about 1/2 an hour. I am asking if the data on the target drive is overwritten since the data on the source drive was erased.
Here's the thing, clonezilla is usually filesystem aware, and hence, its image, only contain areas with data. Empty space is not stored in the image. So when you restore from this image, only the parts that actually contain data are filled, the rest, is left the same.
using dd on the other hand, makes dumb complete disk images, which might be what you want.
Practically this should work OK, however there may be small obscure bits that don't get overwritten - it really depends on how paranoid you are about people possibly getting a tiny snippit of information from you if they are really dedicated.
If you are worried about people grabbing your photos or personal documents it should not be a big deal - provided the entire partition is used. If you are worried that someone might know that once upon this time that drive was used in a particular machine, something like that, then no.
Realistically though, 99999/100000 it would be easier to get the information they want another way (social engineering, beating it out of you, bribery, dumpster-diving, key logging).
I would point out that 40 gig drives would be very old, and likely to start failing, so you may have bigger concerns on your hands soon. (And remember that if a drive starts failing, data can be hidden in the failing parts of the drive which can't easily be overwritten, but might be recovered with enough effort sometimes)