Asterisk IM echo problem

Hi, I have Openfire 3.5.1 running on a Debian etch box, I installed Asterisk IM plugin and created a server (From Admin console).

I want it to make computer to computer calls. When I call another computer (both using Spark 2.5.8) i have a terrible echo. I´ve been doing some reading and I came to think that i need to install Asterisk and use the Asterisk Im plugin to comunnicate asterisk and openfire, am I right?.

Excuse my english I know its not very good.