Can all stock holder get a login information or does dividend paid to private address? What?
The exchanges that ASICMiner trades their shares on require you to register with a Bitcoin address on which you want to receive your dividends.
See this answer on where ASICMiner shares can be traded.
When they pay out dividends, the total amount will be shared equally among all shares and payed of all shareholders by the address they gave the exchange to receive dividends on.
They have a bitcoin address of each shareholder and each week they make a payment to this address, proportionally to the number of shares he owns.
This is one of the div-payment transactions (there are few of them each Wednesday): http://blockchain.info/tx/8e26e8fd5eada1dc5d5125b39db66129bb55645d654b4c6dfc4a0611f3de358d