Reorder Thunderbird account list
First close Thunderbird, because it writes to the user preferences file on exit.
Then open the prefs.js user preferences file in the C:\Documents and Settings\<username>\Application Data\Thunderbird\Profiles\<unique-folder-name>.default folder and adjust the following lines to the desired order:
user_pref("mail.accountmanager.accounts", "account8,account9,account7,account3,account4,account5,account6,account2,account1");
user_pref("mail.accountmanager.defaultaccount", "account8");