I had the same issue and solved it by adding a TabHost on the Activity. You can set the MapActivity as the tab content and hide the button for it.
Example code:
map.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
    <com.google.android.maps.MapView
        android:id="@+id/mapview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:clickable="true" />
</LinearLayout>
main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">
    <Button
        android:id="@+id/menu_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="menu" />
    <TabHost
        android:id="@android:id/tabhost"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">
        <TabWidget
            android:id="@android:id/tabs"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content" />
        <FrameLayout
            android:id="@android:id/tabcontent"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent">
        </FrameLayout>
    </TabHost>
</LinearLayout>
MyMapActivity.java:
public class MyMapActivity extends MapActivity
{
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.map);
    }
}
MyActivity.java:
public class MyActivity extends TabActivity
{
    private LayoutInflater inflater;
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        inflater = LayoutInflater.from(context);
        // Inflate menu here
        // Get the TabHost
        TabHost tabHost = getTabHost();
        // Add the button and content
        TabHost.TabSpec spec = tabHost.newTabSpec("myMapTab")
                .setIndicator("Map")
                .setContent(new Intent(this, MyMapActivity.class));
        tabHost.addTab(spec);
        // Hide the button
        tabHost.getTabWidget().getChildAt(0).setVisibility(View.GONE);
        MapView mapView = (MapView) tabHost.getTabContentView().getChildAt(0).findViewById(R.id.mapview)
    }
}
I hope this solves your problem.