Strange...it shoudn't be that big 255 characters
You can try this query
CREATE TABLE `smf_pretty_urls_cache` (
`url_id` varchar(255) NOT NULL,
`replacement` varchar(255) NOT NULL,
KEY (`url_id`(100))
) ENGINE=MyISAM DEFAULT CHARSET=latin1
Where smf_ is your database prefix
You would then need to remove these lines from install.php
$smcFunc['db_drop_table']('{db_prefix}pretty_urls_cache');
$smcFunc['db_create_table']('{db_prefix}pretty_urls_cache', array(
array('name' => 'url_id', 'type' => 'varchar', 'size' => 255),
array('name' => 'replacement', 'type' => 'varchar', 'size' => 255),
), array(
array('type' => 'primary', 'columns' => array('url_id')),
), array(), 'overwrite');
Then repackage the zip file and install from there.