Use of the PCF8591 is a nice solution for any microcontroller. A simple two wire I2C serial interface, which is rather easy to implement in software, allows you to connect to this chip which offers an 8-bit D/A converter and 4 channels of 8-bit A/D converter. I like these parts because it is easy to place them close to the sections of the board where analogue curcuits are located. There are three "address" pins on this part so it is possible to use up to eight chips on one I2C bus.

Here is a data sheet link:
http://www.semiconductors.philips.com/cgi-bin/p...ip/pcf8591

Michael Karas