Okay you definitely want to go with a collaboration platform, rather than a promotional platform.
Windows Live is at
www.live.com. Live accounts are free (of course), and integrate with Hotmail, Windows Messenger, and MSN. Before you even get into the collaboration features, you also have Office Live, where you can create, edit and manage Word, Excel, PowerPoint and OneNote documents, storing them on SkyDrive, so you can access them from anywhere. Most folks won't even need to buy Microsoft Office anymore; practically all the features you need are available, free, through Live. There is also a photo album feature; again before you even get into the collaboration features that you're aiming for.
What you want is a Live Group. The address is groups.live.com. You've got a group calendar (which can be integrated, by each member, into their own Hotmail calendar), group conversations in Messenger, shared documents and file storage for your group, and a shared photo album.
Again, there are similar services available through Yahoo and Google, but they're limited in ways that were critical for us. For example, Live allows you to send email to the group (i.e., to everyone in the group) instead of just posting messages. A lot of people far prefer to deal with group discussions in their own email client. The other two services rely more on discussions posted online.
Live is going through an upgrade today, so today might not be a good day to check it out, but check into it tomorrow if it sounds interesting.