Try contacting your local architecture institute. If you are in Pakistan, as I gathered from your name, you can write to the Hon Secretary or the President Institute of Architects Pakistan (IAP) at email@example.com
I don't know which institute you are in; as for me in Mumbai, each college has one student representing the college to attend the conference, so I would advise you to inquire in your college if they too got an invitation, which I'm sure they would have.
Well, this is too late to write in this forum. I also have heard about ARCASIA; I am a student from CEPT, India. But when I trained under a Sri Lankan architect called Madhura Prematillake, I came to know about this ARCASIA forum.
The next proposal was made by him, as in the Sri Lankan architects, and the brochure for the same was getting designed at the office.
He had also given some lectures at the ARCASIA 2006. But I doubt regarding the invitation sent to my college. So if it is happening next year, I would be glad if we would be informed for the same.