Here are some links you may or may not find useful:

www.google.com - This is the de-facto search engine these days. Used to be especially good at finding info for Unix/Linux stuff.
http://www.beis.de/Elektronik/Filter/Act3PoleLP.html - Unique page for dimensioning of active 3-pole filters with a java applet. Kudos to Uwe Beis for this excellent tool.
http://www.ada-ware.com/ -Must have utilitiy for getting rid of spyware.
http://www.safer-networking.org/ -Must have utility for getting rid of spyware.