I think the National Semiconductor original data book had some excellent info and diagrams. I used the DAC0808's all the time and had great luck with them. I am currently using a pair to generate sine/cosine signals to form circular traces on a radar system. I generated the truth tables by hand but also found an online calculator where you program the number of bits and number of steps and it will generate the binary truth table for you. The book explains the scaling, offset from zero if desired, and overall gain. If I remember, the 0808 is designed as a variable current source, not a variable voltage source, so some external circuitry will convert the current output to voltage output, thereby requiring the opamp you mentioned with inverting feedback to set gain.