You don't always need the methods described by Kasyan. For example, to open the Index panel, simply do
app.panels.item("Index").visible = true;
The names of the panels you can set like this can be displayed by the following one-liner:
@Pete – for locale independent strings try the "$ID/englishname" method.
For example, in my German InDesign CS5.5 the visibility of the "Articles" panel can be set with:
app.panels.itemByName("$ID/Articles").visible = true;
the German locale for "Articles" is "Artikel", so it's the same for the German InDesign to say:
app.panels.itemByName("Artikel").visible = true;