1: I don't know if the lib work with ATmega324 and I don't know Arduinos with that processor. The typical processor is ATmega328.
2: Have you use level-shifters or does your Arduino run with 3.3V only? If the Arduino is 5V you need level-shifters or you could broke your SD card. The simplest way to build a level-shifter is using two resistors for every of the four input pins at the SD card. A description can be found in file SimpleSDAudio.h.
3: You have to power the SD card as well - connect GND to pin 3 and 6 of SD-card and connect pin 4 to the 3.3V output of the Arduino.
4: If there is no sound try the example BareMinimumWithDebug first and look at the output from the serial port. This can give you an indication if your wiring is still wrong or if there is something wrong with the filesystem on card or the file. You can post this output here in the forum to get more help.
My board has a 5V and 3.3 V.I directly connected the MOSI, MISO, and SCK of the SD card to the MOSI, MISO, and SCK of my arduino.I also directly connected the VCC pin of my SD card to the 3.3V of the arduino.After connecting everything, I checked the voltage at the 3.3V pin of my arduino.I used a fluke to measure the voltage. I got a reading of 4.3 volts.I'll try the 100uF. It might work.Also, I'll try connecting the audio out to pin 9.