If you don’t know about dropbox yet, then go here and get a free (2GB) account.
Then, after you’ve got it set up and know a few things about it, get the beta here; it supports LAN syncing, which is what I’ve been after for a LONG, long time.
At one point, I had three people and 5 machines all trying to download the same 10 files that someone posted into a shared dropbox folder. As you can imagine, this took forever and was hugely inefficient. With LAN sync, the 10 files will download from the internet only once, and then the other machines will all update via the local network.