pb7 setvalue for compute field not working

Friends,

string ls_user

ls_user=get_user();

messagebox("test",ls_user)   ====== this is working..

i tried with two different ways...both are not working..the dw_1 is in the crosstab report.

i want to send this user name either to the compute field or to the datawindow query directly in the where condition...

whichever is possible , pls provide me the solution.

dw_1.SetItem(1,'compute_1',ls_user)   ==== Not working

dw_1.object.compute_1.expression="'"+ls_user+"'"  === Not working..

thanks