waoo i have got it !!!.
thank GOD at last, i have got it.
Well someone else looking for this here is the solution if u are having an unknow command error while using apt.
Firmware 3.0 doesnt have this installed by default when u jailbreak it, so u need to install Aptitude from Cydia, and then if u use apt-get command in Terminal, BOOM, it ll work !!! 😀