HOW TO: Regularly backup Windows XP to Ubuntu, using rsync
Back in September I revived my MiniITX box to serve as a backup server. I set up BackupPC, ran it 
once, it seemed to work, and then ignored it for weeks. When I checked back, it hadn’t run successfully since. Ugh, I want backups to just work! A few nights ago I decided to try again, this time dropping the constraint of not installing software on my laptop. Turns out I already had the building block I needed: rsync, installed in the form of Cygwin. I began with these Rsync for Windows instructions, and everything went smoothly until the very end—rsync on Windows wasn’t connecting to rsync on Ubuntu.
My gut told me rsync’s port 873 isn’t open on Ubuntu, but I had no idea how to open ports anymore. Luckily I found How to start rsync daemon at boot in the Ubuntu forums which told me exactly what I needed to know. How to regularly backup Windows XP to Ubuntu, using rsync - Justinsomnia