how could i interface an 8 ohm speaker with a dac0808?

Answer 1

At a minimum, you will need an audio power amplifier (PA) -- either transistor design, or something like an LM386. If you need more power, a more powerful PA will be needed.

The DAC is a current output multiplying DAC, so it is best to use an OpAmp to convert the DAC current to voltage, then you can feed that signal directly into the PA.

Use figure 1 in the datasheet:
http://cache.national.com/ds/DA/DAC0808.pdf

Then use any of the Typical Applications for amplifiers in this datasheet:
http://cache.national.com/ds/LM/LM386.pdf