A newer version of the applet you are requesting is available as part of a free tutorial on filter design. The tutorial offers the same features as the applet, plus it also simulates the output of the filter. Two versions of the tutorial are available:

Lowpass Butterworth Filter design

Highpass Butterworth Filter design

If you prefer to use the older version of the applet (no simulation, lowpass) you can access it here.

Additional information: the older version is strictly a Java applet and uses frames to control the display of the tutorial text. The newer version uses Javascript and dynamically draws the filter schematic based on the order of the filter. At the last step of the tutorial, the circuit parameters are passed to a Java applet that calculates the cascaded S-parameters of the filter and plots them.