Good project! With I2C inetrface you can work with MAX6651 chip for control and monitoring the fan in linear voltage.See data sheet http://datasheets.maxim-ic.com/en/ds/MAX6650-MAX6651.pdf[/URL]
And for temp. you can use one like MAX6697 see datasheethttp://www.maxim-ic.com/quick_view2.cfm/qv_pk/4597