Goto this URL and click on the RADAR location you would like to display
Look at the URL you have been taken to, it will look something like this
Note the ID - see bold section it will start with IDR then is usually followed by a three digit number.
Open a new sign creator document, double click the background and set the dimensions to 562 wide and 564 height.
Choose Insert in the top menu, then choose Online picture
Type this URL in http://www.bom.gov.au/radar/IDR022.gif
Replacing the IDR022 with the IDR id from the URL in step 2 then click OK.
Double click the image, then under the image tab, add this after the URL, be careful not to add any spaces.
Then change the "Reload image every" to at least 120 seconds.
Go to the "General" tab.
Change the x and y coordinates both to 0
Then change the width to be 562 and the height to be 564
Save the sign creator file, then add to your playlist as normal.