I access my Hotmail through Outlook - I can simply drag and drop it back into my Hotmail account.
But like Ascendancy said, I think when you move it out of your account, it deletes the emails and they'll be in your 'deleted items' folder.....
If they're not, i'd try the Outlook method (assuming you can't do it from Thunderbird, and you can export the mail into an Outlook PST file).