hello
i was struggling for a month for applying residfual stress to a polysilicon
thermal actuator/ which ver of ansys are u using?if you go into the solution
menu there is a command called initial stress. when you click that ansys asks
for the file . you write a file of the stress in note pad and save it. the file
must have all the six componenets of stress. when you click the initioal
stresss command in ansys ansys will ask you to input the file. so just input
the file . then ansys will ask you how it should apply the stess. on all
elements? on ceneter of each elements ? as a constant stress etc. sojust take
constant stress and say ok and ansys will apply it for you.

as to your other question considering the cube i would either select the nodes
in that region so only that part is constrained or else create a separte area
glue it and constrain that area only.
tell me if u get an probs

amar