Do all computers output digital thru USB?


Forgive my newbee question but I want to output a digital signal to my USB DAC from my computer. How do I know if my computer outputs digital thru its USB port or analog? How do I get a digital stream to output to my DAC? Thanks for the look and the help. Really.
128x128pugstub
Go to
Control panel>>Sounds and Audio Device Properties
Click Audio Tab
Change Sound Playback default device to USB speakers

and then click apply.
Just tried it and still can't figure it out. I am using Windows Vista not XP so it seems to be different. can anyone with familiarity with Vista help? Thanks
The computer should set up the DAC as soon as you attach the USB cable. If not, the DAC probably comes with drivers that should be loaded first.