InnoDB should already available. You can check with
mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| CSV | YES | CSV storage engine | NO | NO | NO |
| MyISAM | YES | MyISAM storage engine | NO | NO | NO |
| BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO |
| ARCHIVE | YES | Archive storage engine | NO | NO | NO |
| PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO |
| FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)
or
mysql> show variables like 'have_innodb';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| have_innodb | YES |
+---------------+-------+
1 row in set (0.00 sec)
mysql>
Make sure skip-innodb is not in /etc/my.cnf
Since you are using the InnoDB Plugin, you need to activate new features to greatly enhance InnoDB Performance. For example, did you know there are new options for making InnoDB use multiple CPUs? See my past posts on this:
This is important because there are occasions when InnoDB in older versions of MySQL is faster than newer versions. I wrote about this as well:
Additional Reference from MySQL Performance Blog : http://www.mysqlperformanceblog.com/2011/10/10/mysql-versions-shootout/