i write a oracle stored procedure in login screen.. its two different type of login employee and employer...in front end assign the procedure in class file... how to call different forms

my procedure
cmd = New OracleCommand(" login", con)
cmd.CommandType = Data.CommandTyp e.StoredProcedu re
cmd.Parameters. Add("P_USERNAME ", OracleType.VarC har, 45).Value = uid
cmd.Parameters. Add("P_PASSWORD ",...

how to clear the session fields...and

how to false the post back option in asp.net
send the coding pls