Hi Zaza,
The simplest way without physically modelling it would be to add an alpha layer to the image in photoshop. This will allow the background and all the gaps between the bars to show as invisible. Then save it as a tiff and put it in a loaded library.
You can then set it as a material in ArchiCAD, set the correct size and tick bumpmapped and transparency in the material settings, and apply it to a thin piece of wall the same size.
You will have to play around with the 'Align 3d texture' and 'Set Origin' under the 'Design' menu to align it correctly in the 3d window. See the AC10 help files for more info.
Looking at the image you have though, it will take quite a bit of work to clean up sufficiently to be able to select all the white bits to save as the alpha. Try increasing the contrast several times and/or converting it to black and white in different orders to see which works best. This should save you some work before you start manually editing it.
Good luck!
Pete.