You might want to take a look at this thread (all parts are listed) :
http://www.vdrums.com/forum/showthread.php?t=54170
Here's the Hall Effect sensor I think most of us have bought :
http://www.bitsbox.co.uk/sensors.html
"Hall-Effect Sensor
A1302EUA-T
Voltage output proportional to the applied magnetic field.
Sensitivity 1.3mV/G
Operating Voltage 4.5-6V"
More details here : http://www.bitsbox.co.uk/data/Allegro1302.pdf
And if you look at the picture above, this is how it should be wired :
VCC (Power source) = Tip (Input 3 on Syntex kit)
Vout (output of the circuit) = Ring (Input 4 on Syntex kit)
GND (ground) = Sleeve (GND, Input 1 or 2 on Syntex kit)
Not sure Conrad sales everything you'd need. And for the rest it's up to you to find a way to fix the magnet and the sensor on your hi hat!