Congradulations on beating KH2! I'm glad you liked it!
However, that was not the secret ending. To unlock the secret ending, you have to beat the game in hard mode and complete everything...but I couldn't, so I downloaded it on a site I found on google. (Just look for KH2 UK and it should be one of the first hits...make sure to look for the same things in the link. Then go to the video section for KH2 and it should be in there.)
And the name of the English version of the opening is "Sanctuary" by Hikaru Utada, who did the opening for the first Kingdom Hearts. The Japanese version of it is called "Passion." (Downloads for those are also on that site, but in the audio section.)
I hope I helped...