i2c and a Dallas RTC Anyone??

So when using the Wire library you need to manually hook up a pull-up resistor. I was playing around with the digital lines trying to use the internal pullup resistors and get the I2C communication going myself. I could never even get the first ACK.

Why is the Wire library on the analog lines? Is there something I am missing in regards to the complexity of communication over an I2C interface with arduino?

Do any of you know of any successful attempts at a wire type library using the digital lines?

Thanks!
Lucas