oh man, the white screen of death is the worst. had that happen a few times myself. you definitely can't get to the admin panel directly when it's like this. your best bet is to use FTP. connect to your site, go to wp-content/plugins, and find the folder for the plugin you just updated. rename it (like 'plugin-name_old'). that should deactivate it and hopefully bring your site back so you can log in.