With all these large download sizes as of late, it might be a good idea to get a BitTorrent tracker running. While not ideal for long-term sharing, BitTorrent is excellent for large files hosted for short periods of time. With a lot of people downloading, it's also faster.
If the technical level of users would be a problem, you could offer a small standalone client that fetched that particular days download, ala the World of Warcraft patcher.
Just a thought.