Your MobileMe account was terminated in July. If you did not migrate it to iCloud before 1 August it is too late to do so and the account and its entire contents have been deleted.
You can reactivate the email address (though not its previous contents) by using it to open a new iCloud account: however you cannot do this on Snow Leopard. You would have to get access to a Mac running 10.7.2 or higher, or an iOS5/6 device, and use that to set up your account. Possibly if you asked nicely at an Apple Store they would do this for you.
Once you have an account, or if you did in fact migrate, you can access its Mail on Snow Leopard by following the instructions here: