This isn’t a trivial thing to do — you’ll need to do some serious setup to make this happen. Part of this is because it’s hard to distinguish between downloading and normal web browsing, because they generally take place over the same ports. There are a few things you can try: First, you can take a look at squid-cache.org, which offers a tool that can optimize “web delivery”. You could also try the iBoss hardware (www.myiboss.com) — it’s designed to give you control over the types of activity on your network. It will be difficult to distinguish between download, but you can certainly block things like Bittorrent, music-sharing, and other specialty applications.