You could make an arduino play sounds, but they would not be overly good (Lower quality). An arduino is not really powerful enough for this task. It would also be cheaper to pick up a usb sound card off ebay.
The problem is with the sample speed. So you will need an external DAC. You will also have to write your own driver for the OS to use it. I also have concerns about the serial port being to slow.
People have used arduinos to play music but most use a SD card. A SPI bus is much faster than the serial connection used to connect to the usb port. Also most use PWM, which is 8 bits on the arduino which limits the audio quality. The arduino is only 16MHz so the sample rate for the PWM channel will be lower. This assumes that the code takes no time away from the audio sampling and data transfers are fast. The arduino uses a general microprocessor, so it is not really good at high speed signal processing.