When converting from RedHat to Debian all of the configuration files in /etc should be kept (e.g., burn them to CD-RW). Both distributions use many of the same configuration files, although sometimes they are in slightly different places.
Another approach is to create a parted boot disk (or use a Knoppix CD--knoppix has parted installed) and then create a new partition on your machine onto which you install Debian. This allows you to keep a functioning RedHat install while you set up Debian. Once you have the Debian installation up to scratch you can wipe the RedHat partition and reclaim it for use in Debian (perhaps as /var, /usr). Otherwise delete the partition with parted and enlarge your Debian partition.