Вы должны "обернуть" TabWidget в xml в HorizontalScrollView:
....
<HorizontalScrollView android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:fillViewport="true"
android:scrollbars="none"
android:id="@+id/tabsHorizontalScrollView">
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0"/>
</HorizontalScrollView>
....
и установить в TabHost TabHost.OnTabChangeListener
@Override
public void onTabChanged(final String tag) {
View tabView = tabHost.getCurrentTabView();
int scrollPos = tabView.getLeft() - (tabsHorizontalScrollView.getWidth() - tabView.getWidth()) / 2;
tabsHorizontalScrollView.smoothScrollTo(scrollPos, 0);
}