Picking a Working Microcontroller Clock Source

I recently ordered a batch of parts from Digikey for a circuit board I am working on using the AT90USB162. In my past experiences with the Atmega 8, I simply copied many other peoples designs and got a similar clock source hoping it would work. I never really understood the differences between the different types of clock sources such as a crystals, resonators, and oscillators. When trying to search for a basic tutorial on clock source concepts all I managed to find was a big pile of trash geared towards highly experienced electrical engineers. Right toward the end of picking a clock source I came across exactly what I was looking for at the Society of Robots called "How to use Crystals on Your Microcontroller".

Prior to reading that information I couldnt find anything explaining what the Load Capacitance rating actually meant and how it translated to performance. From what I understand, the lower the load capacitance; the more susceptible your circuit will be to other forms of EMI. On certain clock sources your actually supposed to include two capacitors that match the load capacitance of the source....oops. I had not been doing that in the past.