It was called The Noozles, and the intro for it is in our archive already.
It was a kick-ass toon, wasn't it? One of my favorite Golden Age Nicktoons.
The girl's name was Sandy (I think), the male koala was Blinky, and his sister was Pinky. They came from a universe full of anthropomorphic australian creatures, and the portal to and from this universe was inside of Aires Rock in the Australian outback.