I think there's a Philips application note on interfacing the PC parallel port to the I2C bus?

If you're building an 8051 device to interface to the I2C, I would leave the decoding of the data to the PC; ie, do the minimum processing on your 8051 and let the PC do as much as possible.
This has the benefit of minimising the traffic between the 8051 monitor and the PC (the limitations of Windoze serial comms have already been mentioned).