Action script _root.attachMovie

Hi all!  I have a big problem at work. Here is the situation.  I have an html passing a variable as an array to my flash.  In the flash i want to call a couple of symbols depending on the variable from html and display them as a slideshow. I need to add these symbols dynamically but i dont know where to start.  I have created all my movie symbols and linked them for actionscript.  I have created a simple line of code just to display one symbol using _root.attachMovie and the  symbol does not show. here it the code:

_root.attachMovie(usb, usb,1);

usb.x = 276.15;

usb.y = 199.50;

Now the symbol should be visible right? What am i doing wrong?