This can be done with groupings in Moodle 1.9. provided that you have enabled groupings in Site Administration > Miscellaneous > Experimental.
In the Administration block of your course go to Groups and create two groups (for example, "Bagus" and "Hitam"). Add the students who need access to the assignment to group Bagus and add the rest of the students to group Hitam.
Click the Groupings tab on the Groups page and create a grouping, let's call it "Sateh", and add group Bagus to the grouping Sateh (i.e. in the Edit part of the grouping, click the icon for "Show groups in grouping").
Create your assignment and in the assignment settings at te bottom of the page (in the part called Common module settings), click the Show Advanced button to display the grouping settings. Select grouping Sateh from the drop down list and tick the box "Available for group members only". Then save the assignment.
The assignment should now be accessible to all students in group Bagus, while it will be invisible to students in group Hitam.
I hope these instructions suffice.