Thanks for your response Brian.
how good would it be to use Wordpress blog with built in forum plugins(bbPress), could this be considered as an alternative?
( I need this forum app for limited period/audience... say for 1-2 months, so a light weight app with minimal feature will do )
I've been working with Rails since before 1.2.3 and I cannot recall any packaged forums. Although that was back in the days of the "old Rails engines" so you might have some luck with that... but I doubt you'll find anything.
Unless it is completely impossible I would recommend upgrading your app to 2.3.4