you cannot implement I2C connecting SDA and SCL directly to the port pins. If you read the I2C specs, you'll find that there are conditions like arbitration or clock stretching, where one device pulls the line low, the other pulls the line high. Also in the I2C specs you will see that all devices on the I2C bus are open collector or open drain, and the bus has a pull-up resistor for both lines. The parallel port has push-pull lines, so, connecting I2C devices to it can lead to malfunction, or, in extreme cases to the deterioration of the components (or the port pins). To correctly implement I2C, you can use a buffer that can be put in high impedance (has enable pin), like 74hc125. Connect the input to the ground, and use the enable signal like data. You will also have to use another buffer from the hc125 to read the same line, but for reading you will have the output always enabled. Implement this once for the SDA and once for the SCL, and you have your I2C interface.
Hope you got the picture, if not, PM and i will try to make a schematic for you.