data from itab to be store in text file in desktop

hi

i am tyring to store the data from itab into a text file in desktop,but its now owrking.

i am using open dataset statment,but no where data is storing.My code:

TYPES : BEGIN OF ST_DEMO,

REG_NO(10) TYPE C,

NAME(20) TYPE C,

ADDR(20) TYPE C,

END OF ST_DEMO.

DATA : WA_DEMO TYPE ST_DEMO,

IT_DEMO TYPE TABLE OF ST_DEMO,

L_FNAME TYPE dxfile-filename .

PARAMETERS: P_FNAME(128) TYPE C DEFAULT '\usr\sap\put\vipin.txt' OBLIGATORY.

L_FNAME = P_FNAME.

***

WA_DEMO-REG_NO = '100001'.

WA_DEMO-NAME = 'ANAND'.

WA_DEMO-ADDR = 'NAGARKOVIL'.

APPEND WA_DEMO TO IT_DEMO.

OPEN DATASET L_FNAME FOR OUTPUT IN TEXT MODE ENCODING DEFAULT.

WRITE :5 'REG NUM',16 'NAME',37 'ADDRESS' .

LOOP AT IT_DEMO INTO WA_DEMO.

IF SY-SUBRC = 0.

TRANSFER WA_DEMO TO L_FNAME.

WRITE :/5 WA_DEMO-REG_NO,16 WA_DEMO-NAME,37 WA_DEMO-ADDR.

ENDIF.

ENDLOOP.

close DATASET L_FNAME.

please tell me where is the prob?I wan to schedule it for background job.

regds

vipin