Kevin Unangst, global director of Games for Windows told that Games for Windows - LIVE is also coming for Windows XP, as it is only present for Vista right now.

Unangst said “There is no charge for Games for Windows - LIVE membership, and it offers a multiplayer experience PC gamers expect while introducing completely new functionality to online gaming on Windows. A no-charge Silver membership offers PC to PC multiplayer play, in-game voice chat, cross-game chat, single-player achievements and a unique identity across multiple games.

We do offer a paid Gold subscription that adds features you can’t find on other services, like cross-platform with the Xbox 360, enhanced matchmaking to find gamers of the same skill or rank and the ability to earn multiplayer achievements. Anyone who already has a Gold membership on Xbox LIVE automatically has a Gold membership on Games for Windows - LIVE with their same gamertag. It’s the same network. And for gamers who aren’t Gold already, the subscription is about US$4 a month - and works on both Xbox 360 and Games for Windows- LIVE compatible games.”