If it's just for a backup, you can zip the project, then use "split", which is a command line tool, to split the zip file into parts of a specific size. Burn the parts to multiple DVDs and if you ever need to bring the project back, you'd just "cat" the parts together and unzip.
Now, that's how I would do it, but there are backup tools that will do it all for you. My problem with backup tools is that they often use proprietary methods and if you don't have the tool available, you can't restore the backup. My method uses standard tools that are available on any OS X or Un*x machine.
I suppose that now you're going to tell me you're on Windows! You can get these tools for Windows, but they aren't native. You may find the Microsoft backup utility will work. Hopefully, for your sake, you're not using MS Windows.