>   I'm looking at DAC out to opamp to give right voltage swing and into
> the adj pin on a LM317.  Still need the resistor from output back into

I did something like that in my WISP programmer (
http://www.xs4all.nl/~wf/wouter/wisp ): 4 16x84 outputs via 4 different R's
to the mid of the two lower Rs on the 317 (take a look at the schematics).
I tried to calculate the 317's output voltage for each of the 4^3 settings,
but this was beyond my math and too sensistive to very small variations in
the R's. Instead I just stored the calibration data in the 16x84 which
controls the whole thing. Result: much cheaper than using a real DAC, but a
calibration is needed (of couse you could automate that).

regards,
Wouter.