well u need to suppy the exact filename and make sure that the file is exists or it will not working.....
example:
/tbg 0 2 C:\Documents and Settings\P4P800-F\Desktop\tbg1.bmp,C:\Documents and Settings\P4P800-F\Desktop\tbg2.bmp,C:\Documents and Settings\P4P800-F\Desktop\tbg3.bmp

• it will continuosly animate the picture.
  Well actually what it did was just changing the file u specified. If you familiar with gif animation then you can called the file as a frame.
  So, if the file you specified completely containing the different graphic it will not look like an animation but more look like a image changing. It is better if the file being as a frame. I did this bcoz mirc not supported gif and that means the gif animation cant work with it. So this is my style for making it working.