Conference Call question for a closed VOIP solution

I am very new to the world of telephony. I have been tasked to setup a VOIP solution which will NOT hit POTS or the Public carrier at all. This would be an internal only voip system. Now i know i can use softphones to go point to point but the real necessity is to have several (10+) softphones be able to conference all at once. The setup would be as follows:

1 - 10+ RHEL5.2 workstations
2 - all running ekiga or another SIP softphone
3 - I have opensip installed.
4 - i have asterisk installed
5 - mysql is installed and works with opensip.

Really i was looking for a simple voice conference system and was told about freepbx. Will this do what i need? Do I have too much installed already? Not enough? Any guidance would be GREATLY appreciated!