There is an attribute called android:weightSum.
You can set android:weightSum="2" in the parent linear_layout and android:weight="1" in the inner linear_layout.
Remember to set the inner linear_layout to fill_parent so weight attribute can work as expected.
Btw, I don't think its necesary to add a second view, altough I haven't tried. :)
<LinearLayout
android:layout_height="fill_parent"
android:layout_width="fill_parent"
android:weightSum="2">
<LinearLayout
android:layout_height="fill_parent"
android:layout_width="fill_parent"
android:layout_weight="1">
</LinearLayout>
</LinearLayout>