I have used
BackupPC quite successfully on my home network. You don't have to touch the Windows machine, expect for maybe making a special backup user, but you don't have to do this.
It automaticlly backups shared folders and won't duplicate files on successive backups.
It's relatively easy to setup and only requires SAMBA, Perl, and Apache. You can use rsync if you want to but it is not required. Also, to backup other linux shares you can use tar if you perfer.
LK