$49.99 for a year. $19.99 for three months. $7.99 for one month. That's how much subscription to Windows Live Gold membership will cost in North America, according to a report on Game Informer.
This is identical to the cost of Gold membership subscription on Xbox Live over the pond. Like Xbox Live, a Silver level of service on Windows Live will be free.
We assume that UK pricing for Windows Live Gold will be identical to Xbox Live Gold in this case. One these shores, it's £39.99 for a year's subscription, £14.99 for three months.
What will you get for your money? Well, that's not been fully revealed but it's expected that Gold membership will be required to play cross-platform multiplayer between PC and Xbox 360 - with Shadowrun, for example.
In addition, it's recently been made public knowledge that with Halo 2 Vista, a Gold membership lets players earn achievements (a points system for bragging rights, essentially) in multiplayer as well as single-player. You can play multiplayer with a Silver membership, but can only earn achievements in single-player.
Game Informer's report goes on to say that existing subscribers to Xbox Live Gold automatically count as subscribers to Windows Live Gold, adding that your "gamer tag and achievements will be used across both Xbox and Vista PCs."