The Arduino IDE works for library development, but to make one, you MUST have a .pde file. You could then use the left pointing arrow at the top left side and then choose New Tab. Then you can choose a file name and the wanted extension (.h or .cpp). As sad, this MUST have an .pde file. If you don't want that you can use another IDE like Qt Creator or Eclipse. I use Qt Creator and it works great. There is one commercial and one non-commercial version available of the Qt Creator.
The Arduino IDE is perfect for library development.
for a complete tutorial.
That tutorial is of course good.
ALWAYS remember you must put #include <WProgram.h> on top of both your header file and source file.