preventing "back" button usage?

Sorry to plague this list with questions today, but I was hoping someone could help me understand a fundamental thing about how browsers work -- how can I achieve the effect that many ecommerce sites (such as Amazon) use to prevent the user from going "back" in their history? For obvious reasons, I would like to avoid JavaScript to achieve this feat. I have some multi-part forms that I do not wish users to be able to repeat accidentally. I believe it has something to do with a header and the browser's cache, but I really don't know anything about it. TIA, Erik ---- Erik Price Web Developer Temp Media Lab, H.H. Brown pricee@hhbrown.com