You will find all you need in the Philips appnotes, the information range from the IIC standard to simple code snippets. The address of the list can be found under "intersting sites" in links (left) - just realized that links is German for left could'nt help including that information - not trying to translate, just telling you where to look - anyhow the actual code described in the appnotes can be downloaded from http://www.semiconductors.com/products/standard/microcontrollers/download/80c51/index.html

Erik