Rdiff-Backup provides a fairly nice way of backing up a server, and I have used it to back-up a number of different servers, each with a different version of rdiff-backup. This is annoying because although a version 1.1.15 should work with 1.1.12, for example, in reality it does tend to complain.
Because of this version-skew on different types of servers, I took the approach of having multiple versions installed on the backup server (Mac OS X Panther in the first case, and now Leopard). This document details how you can house multiple versions of the rdiff-backup server on the same machine and use a different version per-client.
You can find the documentation and supporting files in the Files section.