For those who are reading this Post. This is about my Arduino Duemilanove working with a Sparkfun SPC1000 Pressure Sensor.
The code listed beneath in this Post is working OK. Except that the temp in C is a bit high. If you devide by 30 instead of 20 it is more realistic.
temp_in = read_register16(TEMP);
temp_in = temp_in / 30;
// temp_in = ((1.8) *temp_in) + 32; Add this to measure in Fahrenheit.
Serial.print("TEMP C ["); // Change C in F if above is applied.
Serial.print(temp_in , DEC);
Serial.println("]");
As a remark on the 3.3V. It has to be added to the Sensor.
But if you use a LD1117V33 voltage regulator you can support this with the 5V from the Arduino board and has 3.3V available for the SPC1000.
connect the following SPC1000 ports to the Arduino Duemilanove
DRDY - not connected
CSB - I/O port 10
MISO - I/O port 12
MOSI - I/O port 11
SCK - I/O port 13
3.3V - Vout of the LD1117V33
GND - Groud
I've had it running in 15 min. Great. 
Greatings from the Netherlands.
DOSER.