extracting data from a message

MAIN PRPOGRAM : ZPROG1

TRANSACTION : ZPROG2

IF WE RUN THE TRANSACTION CODE , IT WILL SHOW THE *PURCHASE ORDER NUMBER AND GRN NUMBER* IN THE STATUS BAR AS A MESSAGE................NOW I HAVE TO RETRIEVE THOSE TWO VALUES FROM THAT STATUS WARNING MESSAGE AND ADD THOSE DATA TO THE CUSTOM TABLE BY CALLING THE TRANSACTION FROM THE MAIN PROGRAM... HOW TO STORE THOSE VALUES SHOULD I USE GET AND SET PARAMETER ID..........PLS EXPLAIN.......

WITH ANTICIPATION AND REGARDS,

SYED