I see. I might suggest InkScape. It is an OpenSource tool compatible on Windows and Mac OS X (using X11) that has similar functionality as Adobe Illustrator. You may use the Trace Bitmap feature to create vectors from bitmap and image files. It is best to do some clean up inside Inksape and then export as DXF. You may then import the DXF file into ARCHICAD and use the steps to create a Symbol Fill.
If I can find some time (chances are low right now; maybe in January) I will see if I can write up more precise instructions. But hopefully with that, it is a good start for you.
I hope this helps.
Best regards,