Hi Regardv,
On my system (Ubuntu 8.04, i386), the SpaceNav is working nicely with Blender. I tried with the 2.46, 2.47, 2.48(a) versions that you can download from
www.blender.org. Are you sure, the 3dConn plugin is in the correct location?
Mine is at /home/<you>/<your_blender_location>/plugins/3DxNDoFBlender.plug.
If I rename this plugin, the SpaceNav stops working, so definitively it is active. And yes, 2 icons appear in Blender, to set the mode (flymode, rotate) and switch preferred axis.
Are you sure that you start the version of Blender that contains the plugin? If you have installed Blender via the Ubuntu repository (it is an old version), typing 'blender' on command line might start that version. To make sure, go to your blender directory (same as above) and type ".blender". The <dot> makes sure you will run the "blender" program from that directory, and not the one installed by Ubuntu rep's.
Do you activate the SpaceNav daemon BEFORE starting Blender? Some other threads in the forum might also help. Goodluck.