6. Account Cancellation
How do I remove my Hotmail account?
Currently, the only way to permanently close your Hotmail account is to refrain from signing into it for 60 days. Accounts are automatically purged from our servers after 60 days of inactivity. If you need your account to be removed for any reason, do not sign into it again and it will be automatically closed after 60 days.
Bus afraid there is no other way, might be worth removing their accounts from Outlook express or whatever you use, and use your ISP e-mails instead. If you reregister using a different hotmail account, the spam will just start again no doubt.