Line 59 of the file app/code/core/Mage/Install/Model/Installer/Db/Mysql4.php

Replace:

public function supportEngine(){    $variables  = $this->_getConnection()        ->fetchPairs('SHOW VARIABLES');    return (!isset($variables['have_innodb']) || $variables['have_innodb'] != 'YES') ? false : true;}

with this:

public function supportEngine(){    $variables  = $this->_getConnection()        ->fetchPairs('SHOW ENGINES');    return (isset($variables['InnoDB']) && $variables['InnoDB'] != 'NO');}

Or don't do a core-hack! You should override the Installer-Model softly before Installation:

Paste this in your app/code/local/Company/InstallBugfix/etc/config.xml:

<?xml version="1.0"?><config>    <modules>        <Company_InstallBugfix>            <version>0.1.0</version>        </Company_InstallBugfix>    </modules>    <global>        <models>            <installbugfix>                <class>Company_InstallBugfix_Model</class>            </installbugfix>            <install>                <rewrite>                    <installer_db_mysql4>Company_InstallBugfix_Model_Installer_Db_Mysql4</installer_db_mysql4>                </rewrite>            </install>        </models>    </global></config>

And following in app/code/local/Company/InstallBugfix/Model/Installer/Db/Mysql4.php:

<?phpclass Company_InstallBugfix_Model_Installer_Db_Mysql4 extends Mage_Install_Model_Installer_Db_Mysql4{    /**     * Check InnoDB support     *     * @return bool     */    public function supportEngine()    {        $supportsEngine = parent::supportEngine();        if ($supportsEngine) {            return true;        }        $variables = $this                     ->_getConnection()                     ->fetchPairs('SHOW ENGINES');        return (isset($variables['InnoDB']) && $variables['InnoDB'] != 'NO');    }}

And enable the extension. The advantage is, that the old validation is still correct, if the mysql-version is older.

ver 1.9.1.0 downloader.php

Putting this up for anyone thats using the downloader.php currently bundled in the 1.9.1.0 installer.

If you're happy that your MySQL Database does support InnoDB (It's the DEFAULT) in later versions. You can safely edit the file to remove the check and all the download to take place.

    /**     * Check availabe InnoDB on database.     *     * @return Magento_Downloader_Validator     */    protected function _checkDbInnoDb()    {        if (!$this->_connection) {            return $this;        }        $this->addMessage('Database server supports InnoDB storage engine');        return $this;    }