ludvic, what operating system does your file server currently run? If you're using linux you can download cygwin ( www.cygwin.com ), install rsync, set up an rsync server on the linux box and create a quick bash script to synchronize files on a nightly basis and it would be run using the windows scheduler. I also think you may be able to download a windows based rsync server if you do a search. If you want to go this route, I will give you help with the proper syntax, just let me know which rsync server you decide to use.
Also, if you (or anyone else) is looking for an off-site backup, the place where I work (Wiktel) has a new service which works awesome for windows users. The pricing is $10 per month for 1 gigabyte and $20 a month for 3 gigabytes. You download the software, select the files you want backed up, select the time you want the backup to happen and it will be set to do it automatically. It also uses rsync and the great thing about rsync is when you change files, it only transfers the changes and not the entire file again so backups are quick. We also allow people to get old files which are up to 30 days old so if you change a file and decide you don't like it, you can always pull an older version off the backup server.
You can get more information about that here: http://backup.wiktel.com If you're interested in signing up, just send me a PM. It would be wise of those who do not to an off site backup to start doing it...especially if you have important files that would be a disaster for you if they went missing.
I did a lot of programming on the client front-end. It uses .NET and C#.