Do you know when it changed or where i can find ( if it exist) documentation from the very begining?
Some technical details of Bitcoin implementation (Bitcoin-Qt) was never documented. At best, someone could point you to old discussion or relevant part of the source code.
I see on the history of this forum dates on begining 2010 but the peoject started at least in 2007 and the white papee was published in october 2008. I saw program go live in begining 2009.
There was Bitcoin forum at
http://bitcoin.sourceforge.net/boards/index.php. You could find something using web archive service such as
https://archive.is/ or
http://wayback.archive.org/, but i wouldn't expect much if i were you.