This is pretty exciting stuff for serious PC and XBOX gamers, looks like Microsoft are working on cross-platform gaming between the two via their "Live For Windows" project. The first giveaway was discovered as per this paragraph in an article over at the DailyTech :-
A new trailer for Shadowrun displayed a tiny banner of text near the end of the video which read, "Cross platform play requires Xbox Live Gold account and hard drive (on Xbox 360), or Games for Windows - Live Gold account (on Windows)." Clearly, Microsoft has plans for cross platform play between its console and the PC, and the notice of there being a "Gold" account for the Windows platform indicates a premium, paid tier of service.
Get the full rundown on it here.
Even at GDC, Microsoft remained quiet on details surrounding Live for Windows, though Game Informer has learned that the pricing for Live service will be consistent across the platforms. That means that a yearlong subscription of Gold is 49.99, one month is $7.99, and $19.99 for three months. The Silver level subscription will be free to all Live for Windows users, though it will be limited in features, such as cross platform gameplay, compared with the Gold level.
Those who have existing Xbox Live Gold subscriptions can carry over their memberships to work on PC games with all Gamertags and Gamerscore. Achievements are also expected to be worked into Games for Windows games, with Halo 2 expected to be one of the first games to incorporate the gameplay incentive feature.