Electri-fire - check out this protoshield mini-project I put up on the Make:blog. It's just an R/2R DAC without a buffer or anything special, you might find the sine generator sketch @ the bottom interesting.
http://blog.makezine.com/archive/2008/05/makeit_protodac_shield_fo.html?CMP=OTC-0D6B48984890
To play a waveform - set up an array containing bytes that make up the wave you want
then you can write each byte to pins 0-7 all at once with "PORTD="
the time in between each byte can be variable determined by an analogRead value
I guess that's the extent of my current technique 