AVR-Chat

Hello,
  I'm interested in implementing a super cheap DAC (1 or 2 resistors 
and a capacitor) on an output pin of a Tiny 11 AVR.  This AVR has no 
Pulse Width Modulation register/timer that would normally be used to 
implement a pseudo-DAC like this.  
  Any anyone done this?  Are there optimal resistor/capacitor values? 
I'd like to make an adjustable very low frequency oscillator (0.1 to 
5 Hz triangle or sine wave) between +2.5 and 4 volts.  I'd also like 
to make its speed controllable by changing the external system clock 
speed that is fed into the Tiny 11.
  I'm not even sure what keywords to use for a Google search on this 
one.

Thanks,
Alan Probandt
Portland, Oregon USA