I've tried to clean up the thread... I can't see any unposted posts lingering somewhere though.
Example 2: A nymph advances by taking 6 levels of druid. This advanced nymph now casts spells as a 13th-level druid.
@RUMBLETiGER; Definitely. I think its in the Monster Manual section for advancing monsters, but this I'm positive of. Mind you, I don't think there are many monsters (at least in MMI that this is appliccable to, perhaps just Nymph, some dragons and Driders).
edit: MMI p294, under the heading "Asociated Class Levels".