Best automatic backup software over a network and USB?

I'm doing a little research on software for work. We need a small automated data backup solution for 5-15 computers where we are constantly editing and uploading data. Preferably open source (we're an academic lab).

I'm looking for software that runs on Windows and Mac and will automatically sync selected files and folders to an external hard drive and also to a location over the network (shared drive on a PC, for example). Its very important that the program is automatic (background would be best) and reliable. Someone recommended Bonkey, but I'm having crashes with that program, so alternatives would be welcome.

Thanks in advance!

sorry, just found this thread:

Comments pertaining to my specific situation would still be welcome. We can't use online data backup services like JungleDisk or Dropbox due to the sensitivity of our data.