Major Nelson. Previously, any lapsed Gamertags -- caused by changing a Gamertag or closing an account -- went to the infamous Xbox Live "graveyard," never to be used again. Now Microsoft is reanimating the "zombie" tags and offering them up for use once again.
Major Nelson notes that the process "will take some time to complete," as more trashed tags are converted for reuse daily. He advises users to "check back regularly" to see if a desired tag has been resurrected.
Xbox Live memebrs can change their tags in the profile section of the Xbox Dashboard (pictured). The cost of changing one's Gamertag, regardless of whether it's a revived tag or a brand new one, is 800 points ($10).