First does your server meet these specs. 

SERVER REQUIREMENTS

If you plan to host your site elsewhere make sure your host meets the following hosting requirements:

Linux/Unix/Windows

Apache 2 or higher with:mod_rewrite on

mod_security (strict configurations) off

PHP 5.3 or higher with:cURL on

fopen on

register_globals off

safe_mode off

suPHP off

suApache off

suhosin off

PHP modules:

PDO

DOM

mbstring

zip

zlib

ftp

json

MySQL 5.0 or higher

GD Library 2 with FreeType support

Mail server (SendMail, Exim or other)

Cron

as far as the form goes i think that might be part of mod security rules, which usually affects forms.  

From what i understand 1.7.3 is alittle more sensitive to mod security than previous versions so you might want to check that out. 

you can wait for a team member tomorrow night, or you can try to download the software and do the manual install and make sure the tables are MyIsam tables. 

I would find out why your server does not support MyIsam, call your hosting company and ask them why.   

DROP TABLE IF EXISTS `ow_base_user_online`;CREATE TABLE IF NOT EXISTS `ow_base_user_online` (`id` int(11) NOT NULL,  `userId` int(11) NOT NULL,  `activityStamp` int(11) NOT NULL,  `context` tinyint(3) unsigned NOT NULL) ENGINE=MyISAM  DEFAULT CHARSET=utf8 ;

as to the error with the forum, while creating new section in the forum, please open  a firebug console in the Firefox browser and see if there's any error, they are usually red ones. make a screenshot of the error and provide it here. 

Changing the code is not a solution. Change your default storage engine from InnoDB to Myisam, if you don't know how to do that, contact your hosting provider, if they do not know how to do that, I recommend you to change host. The server should be compatible with the software not the opposite.