It depends on the resolution of the Display device and the resolution of the source material (this is the same for HDMI, DVI or VGA) and how you define seeing an HD picture!
A PC is perfectly capable of playing back and outputting various HD source files.
You can connect the PC via VGA to a display that is compatible with an HD signal but has less pixels than the source file (the display will down scale the signal), more pixels than the source file (the display will upscale the signal) or the same number of pixels (no scaling at the display).
Joe