interested to do　　 对做某事感兴趣，想了解某事。
interested in doing　 对某种想法感兴趣，doing 通常为想法。

• I shall be interested to know what happens.
  我很想知道发生了什么事。 (想了解)
• I'm interested in working in Switzerland. Do you have any idea about that?
  我对在瑞士工作感兴趣。你想过这事吗?　 (一种想法)