UK-based Game Domain International is launching their AWOMO service that will allow you to play the game before it's done downloading. As an added incentive to get people to sign up, you can try out the beta now and get Rome: Total War for free.
"The trick, according to GDI, is its 'unique technology' that 'lets you start playing before the game has finished downloading, meaning you can be up and running, jumping and fragging in minutes rather than hours.' Although some other download services allow you to start playing a game before it's fully downloaded, you usually still have to download a big chunk of data before you can start, and GDI reckons that it's cracked this problem. According to GDI, AWOMO takes a look at your PC's spec and connection speed, and then hooks you up with a sufficient buffer to stop your game stalling during gameplay. The company is confident that 'the delivery system accurately predicts the data you require next and ensures it's already there waiting before you need it.'"