If you have minimized both the ISO and the aperture, the shutter speed is what it is unless you put on some neutral density filters or a CP filter.
1/30 or so should be good enough for panning practice. What was your target? If your target is not moving fast enough for your light conditions, try getting closer, which will increase the angular velocity (or something like that).
Since you are shooting a moving target, you will want to be using AF-C instead of AF-S. That way your target remains in focus as it goes by.
---------+---------+---------+ Joseph K Seattle, WA, USA
My 7-year-old ran back-and-forth (hopefully this isn't considered child abuse). And just as you said, I got a much better effect when I moved closer. Still wasn't fast enough, but got a couple of pictures that might pass for panning.
Thanks for the tip on AF-C. Should I also change the auto-focus area from Single-point to Dynamic?