> My latest project involves a PIC16C73A , which amongst other things,  drives
> a serial 16bit DAC. This gives me a control voltage  programmable from 0  to
> 10V.
> I also need to generate a sinewave of nominally 1KHz. The p-p amplitude
>  must track the DAC voltage and be always 10 percent of its DC  voltage.

Do you need the control voltage for anything else, or are you just looking
to have a finely-adjusted sinewave amplitude?  If you're trying to produce
an amplitude-adjusted sine wave, one approach you might consider would be
to generate two 1KHz sine waves in different phases (the phase difference
will set the net amplitude).  I don't know exactly how much precision you
could hammer out of a PIC that way, but it should be possible to do pretty
well (I use that trick in my music box, btw).

Alternatively, since your sine wave frequency is fixed, you could probably
use a simple gating circuit to convert your DC signal into a square wave,
and then feed that through a 4 or 5 stage filter.  Since the frequency is
fixed, you could optimize the RC's so as to give the best possible 1-1.5KHz
cutoff and if you use an active feedback filter you could even add some "Q"
to make your sinewaves really gorgeous.