> So halfway through Missy Elliott's song "I'm Really Hot" the beat completely changes to a faster, jazzier sound. I know it's taken from a track I heard many, many months ago. The hook of the original song went "You're a superstar". I've been looking for this song for a while, anyone know it?

you may have an answer by now, all I know is that it is a HOUSE MUSIC song called "HOT". You might want to google it or ask a DJ who knows house music. It's a very popular, old song.