DC is just extremely low frequency AC...

You have a point

you won't get flat DC with an RC network. but you can get arbitrarily low
ripple. how low do you need it and what settling time can you accept when
changing levels...

I will give you more of an idea on the work - I'm replacing the pots in a
radio control transmitter with a microprocessor so i can interface with a PC
(instead of making a custom Tx which is beyond me and more expensive). I'm
not sure on the minimum ripple (dont want the servos twitching really but
I'd hope to have approximately 100 possible throttle 'positions', the pot
will produce infinitely variable output i know but the servos dont have
infinitely variable positions IIRC. Either way it wont matter if the servos
'twitch' a tiny amount, so long as the response time isnt too slow. Response
time - somewhere 20ms. I can investigate further- unfortunately my analogue
circuit knowledge is poor (im trying to learn!) but my microprocessor side
is OK :-)

Thanks for your help!
James