Thanks Mike.
I did not see any references to lunacy so I'm going to give this a go! ;D
The question of which digi-pot to use is still a bit undecided, the MCP42010 includes two pots and can be daisy chained plus its relative inexpensive. Another possibility is the ad5203 which with four pots can drive four 555s. At double the price it does give double the functionality. SPI seems the only affordable option though?
Is SPI handled much the same as the 74hc595 e.g latch,data, clock, data,clock ... etc etc?
Cheers for the links, they make decoupling quite clear and also the explanation of the L298. Is there an IC that provides a 0 1 output for a 0 input and a 1 0 output for a 1 input so that I only need one pin from the mcp23008 to set direction for a motor? :-?