After originally announcing they'd no longer support activation on new PCs after August 31, 2008, Microsoft has opted to extend support for files sold through their now dead MSN Music service. Here's the details from the MSN team:

On April 22, Microsoft notified you that as of August 31st, 2008, we would be changing the level of support for music purchased from MSN Music, and while your existing purchased music would continue to play, you would no longer be able to authorize new PCs and devices to play that music.

After careful consideration, Microsoft has decided to continue to support the authorization of new computers and devices and delivery of new license keys for MSN Music customers through at least the end of 2011, after which we will evaluate how much this functionality is still being used and what steps should be taken next to support our customers. This means you will continue to be able to listen to your purchased music and transfer your music to new PCs and devices beyond the previously announced August 31, 2008 date.

Microsoft continues to recommend that you back up your music on CD or hard drive along with other important data.

Sincerely,
MSN Music team