What you have there is a "raw" CT. The output of the sensor sold there (part number SCT-013-000) is a current output sensor. This means when 100A is going through the "primary" coil, the leads will excited to deliver up to 33mA of current.
First off, you need to convert this to a voltage - luckily all this takes is a resistor. 100ohms is a great starting point. Connect it across the CT.
You will receive the exact AC waveform current as a voltage. Next in line, you should perform a DC block - a capacitor sized appropriately to pass 50/60Hz. A 47uF electrolytic works.
Next up is the voltage gain stage. Depending on your resistor, you will receive a small voltage (peak to peak) signal. The SparkFun board you have listed will not work for you directly - you just need an op-amp, not a whole measurement IC. You ideally want to use an op-amp in an inverting configuration, as shown here: http://en.wikipedia.org/wiki/Operationa ... _amplifier
The resistors need to be sized to add the appropriate gain from the op-amp. Read the Wikipedia section several times through - in fact read the whole article
. Keep the resistance of the resistors higher (10k-100k).
Now you have a signal to send to your A/D unit. This will be an AC waveform. In order to determine the actual current, you need to oversample this value (preferably 256 times per cycle) and perform an RMS (root mean square) calculation.
Here is a great app-note from Atmel on building an energy meter on an AVR:http://atmel.com/dyn/resources/prod_doc ... oc2566.pdf
Page 36 has a schematic and page 37 has the BOM.