If you change the url from profile.php?do=addlist&userlist=buddy&u=xx to profile.php?do=addlist&userlist=friend&u=9&friend=xx, then the check box that says "Also send a friend request to xx" is already checked, but you still need to confirm the action.
code in memberinfo, if user is friend, then show all friend, if not a friend, show add as a friend, how to make this thing in postbit? is it need a plugin again?
I'm not sure if you'd need a plugin, but I know you will need to replace $prepared with $post if you are going to use it in the postbit template. And, $block_data is also not going to be defined in the postbit. And, those css classes I don't think are defined in a regular vb page either (only on the member.php page).