Ok, here is a ranting and raving post on how to do it. It is obviously 
a dope fiend who have witten it, but he has probably personal experience 
with the method - therefore I include it here. I have divided the text 
into five paragraphs for clarity's sake. 

Subject: Re: Codeine sulfate to morphine sulfate
Newsgroups: alt.drugs.chemistry

[Summary]

you turn the sulphate into anhydrous and then cook it
with pyridine HCL and then coagulate out the crap at pH 9 to 8.75 then
filter it out and one or two drops of HCL 33% will seed the morphine out
which is caught on a filter paper dried and treated with acetic anhydride.

[Pyridine HCl]

Pyridine HCL is made, pyridine must be obtained and placed in a beaker at a
ratio of 10ml pyridine to 12 1/2 ml HCL you draw a line on the beaker at
the pyridine level which is place in first then the correct ratio of HCL
(hydrochloric acid) then boil down the volume to the line you wrote on the
beaker and then cool it will crystallize to a white wax which is pyridine
HCL. 

[Codeine freebase from tablets]

You need codeine power to cook with also which is easily extracted
from codeine and paracetamol tablets, say they contain 8mgs each you'll
need 600 to make 25ml (25 knock you on your ass blasts). The codeine is
extracted by dissolving the chalky tablets in water then filtering out the
chalk.Make up a caustic solution 3tablespoons to 200ml of water and add
30ml to the codeine/water mix then add 50ml of chloroform and shake and
allow the heavier solvent to sink to the bottom then you must separate off
the chloroform layer, don't be too fussy yet just get it out, wash again
with 30ml of chloroform, take it out once dropped then yet another wash and
same remove it. Now you must separate all the water from the solvent every
last little I mean fuckin all of the water must be out, and you can pipette
it or use a separator( a flask with a tap so you shut it off when the water
gets close to running through) then evap off the chloroform in a water
bath, a pot with water in it (simmering) and a plate siting on top  and tip
in chloroform and watch codeine appear as it reduces out (you want white
codeine not brown or yucky looking or sticky). Always use glass, everything
glass and clean well washed clean clean clean. 

[Morphine from codeine]

You need to then measure out say 3gr of pyridine HCL for one and a half grams 
of codeine and melt it (the P) in a long boiling tube (big test-tube) when 
melted shoot in the codeine and it all must dissolve so swish it, and 
immediately stopper the tube with a tightly rolled paper bung. It will turn 
colour and viscosity and it is hard to tell when it's cooked but a yellow/pink 
but not brown takes about 5min with 1 to one and a half of good boiling the 
temp has to hit 230celcius and it's done but it will stick to the sides of the 
tube when ready. Then tip the lot into a clean beaker with 100ml of water in it
then tip some water back into the now cooler test-tube and rinse all of it
out into the beaker. Next add caustic solution drop by drop till you get to
pH 14 (take about 3ml of the solution I said above). You need pH papers,
now wash the solution with chloroform say 40ml shake well and allow to
settle or centrifuge (spin), pipette off the top aqueous layer. Then drop
the pH to 9 and shine a touch through it you'll see it thicken with this
brown mud like shit don't go past 9 add one or two small drops once you
hiyt 9 and filter that crap out, you need a vacume filter with really good
filter apaer for this bit as this stuff is all the shit. When it drops
through after being filtered it will be lighter in colour and may morph
immediatly but tip it into a beaker and check the pH you want to go no
lower than 7.5 (using HCL spirits of salts,hydrochloric acid) while it gets
to 8Ph start rubbing the sides of the beaker with a glass rod or handle of
a wooden spoon right in the liquid at the water level rub hard on the
beaker glass and morphine will seed in clouds off crystals, then filter
them out and dry high above an element on say a fish slice (leave the dope
on the filter paper and dry it then it is easy to get off it flakes off in
chunks).

[Heroin]

then place in a spoon and add acetic anhydride and cover with
tinfoil and bake in the oven at 80celcius for at least 1 hour uncover turn
the oven off and allow the last of the AA to sweat off. Then when cold move
to the top element and heat till at least 80 degree's and sniff well and it
shouldn't sting your nose if it does heat it lightly till the smell goes
and there you have got heroin. 