I agree with oric_dan(333) here. Your schematic is wrong.
BTW, this project sound interresting. I was planning to make a breath analyser using the Arduino. A device like that will be usefull, because I don't want to lose my drving licence / driving job.
First. When you are planning to build a project, you always download / get a datasheet. So I check and here it is : http://www.sparkfun.com/datasheets/Sensors/MQ-3.pdf
Did you read the datasheet ? And the sensor is only $5.00 anyway.
Let see... GND to gnd <-- That is easy
+5 V to H <-- H is heater @ 33 ohms --> 5 V / 33 ohms = 150 mA <-- bear that in mind
A1 + A2 = Connect them together and B1 + B2 = Connect together
A1-A2 OR B1-B2 connect to +5 V <-- your pick
Take A1-A2 OR B1-B2 to any analog pin <-- the left over to the analog pin
And connect a resistor of 47 K to 100 K between analog pin and gnd. <-- the analog pin you pick.
That it.
Program, test for a value, get drunk, test your breath. 