Please Help in secnario setting?

I am new to Asterisk…i was using Asterisk32, before i was established a call using G711 (using X-lite) between my two laptops that are connected in ad-hoc fashion. now i want to do the same thing with speex codec, please help me as when i try this…the asterisk32 gives error that unknown codec…please please help me…i want to use this in my project.
thanks in advance