Gavin:
The I2C diagram, as simple as it is, can easily be misinterpreted. This is a bit hard to describe without a drawing but here goes. On the SCL and SDA lines the horizontal lines to the right of the resistors should end at the bottom of the vertical lines going to Vcc. Or, better yet, the resistors themselves should just replace the vertical lines. As it is drawn now you have three Vcc lines above the ground on the right side of the drawing.
Don