I seem to remember people saying that E-powers are interchangeable with classic powers; like an E-druid can take a classic at-will attack, and vice versa. But I can't find anything to that effect in HotFK, so I'm hoping the community can either confirm or deny this memory.
Look at the keywords. Class name, level, Type (A/E/D/U). If they match on all three points then they are treated as any other power that has all three points matching. If the power just says "Knight attack" with no level listed then they can't be taken as a power with a level.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.