.fbx is a file format for 3D Studio Max and Maya, which have both been acquired by Auto Desk
FBX is an excellent file format for transmitting 3D modelled objects from these programs and will translate straight into Cinema 4D. It however is not supported by ArchiCAD. .3ds and .dxf are however.
You can download a plugin which, allows you to view .fbx files in Quicktime (which works on Windows and MAC) from Autodesk's Website.
You can Also download a converter which, works on Mac Linux and Windows from the same website.
They both require you to register your details with AutoDesk.
Using this converter you can convert an FBX file to and from the following formats. OBJ, 3DS DXF files. To get an FBX into ArchiCAD you will need to convert it into 3DS format and then use the 3DS importer addon to open it as an object in ArchiCAD. This works but has the drawback of making all the Geometry into Simple Triangular Meshes.
The link to download these programs is here:
http://usa.autodesk.com/adsk/servlet/mform_proc
