Microsoft announced that the oldest Xbox live accounts get Xboxes, I don't think I qualify, but how do I determine how long I've been a member?
The easy way to tell the age of your Xbox Live account is by viewing your Gamercard from the Xbox Guide.
You can view this info on any of your friends' (or recent players') Xbox Live profiles as well.
As far as the 10th year anniversary promotion goes, they are sending these out to people who have been Gold members since the beta, so unless your number reads 10, you're unlikely to get one :)
The sweepstakes, on the other hand, is open to everyone with Xbox Live. Just download the gamer pic to enter. Further, you can get a second entry if you're a member of Xbox Live Rewards, which is free and has other monetary benefits.
Microsoft is sending e-mails out to "loyal members of Xbox LIVE." I received one yesterday, and they may be still sending them out.
If you have an Xbox Live Gold Account, you can get look at your account billing history in the "My Account" section at http://live.xbox.com.
The entry to the contest is in the link below. It is open to "eligible Xbox Live members", so it may give you an error if you have not been a member long enough:
To consider yourself eligible you will need to have had an active Xbox Live account on the first Xbox for at least 3 years before the release of the Xbox360, as the Xbox360 was released in 2005.
I've been unable to find anything in my account listing that just simply spells out how long it has been since I signed up.