proc GLM with R

I want to migrate from SAS to R.
I used proc mixed to do comparison between multiple groups and to perform
multiple comparison between groups since, as far as I know, proc mixed does not make assumptions about the data and so 
it is better than a simple anova (data must only be normal).
Es. how can I translate a code like this (two way anova with a factor of 
repetition) :


proc mixed;
class kind  PEEP codice;
model PaO2_FiO2 = kind PEEP kind*PEEP;
repeated /type = un sub=codice;
lsmeans kind*PEEP /adjust=bon;
run;

codice is a unique identifier of patient
kind is a variable which subdivided the patient (i.e. red or brown hairs)
PEEP is positive end expiratory pressure. These are the steps of a clinical
trial. Patient did the trial at PEEP = 5 and PEEP = 10

Thank you

Massimo Cressoni

run;