In this tutorial, I have an ancient Fedora Core 3 machine that I need to turn into a Debian Etch machine. The machine is 600 miles from my home office so traveling to put in CDs is not an economical option.
Read it here
You'll need to make sure your swap space is adequate. We will be loading the base Debian system into the space currently allocated for swap, so you need to make sure you have enough room to accomplish this task. In my case I used 371M of space out of a 1012M swap when the Debian base was loaded, leaving me 590M of free space.