For those of us who aren't soooo familiar with analog circuitry, there is a nice paper from TI with some design information, help, and hints: http://www.ti.com/lit/sl/slyt701/slyt701.pdf

Although many things can be done in "digital" nowadays, analog buffer and filter circuits can be needed and may greatly improve precision and signal quality when placed in front of an ADC or behind a DAC. The TI paper gives many answers and sheds light on some common problems and trade-offs.