No mealea,
You need a 16 bit or a 32 bit displacement map. Never a jpg.
In zbrush, a 16 bit B&W PSD or tiff file is required.
Now enjoy the bad artifacts on your new posted artwork.
It is not the first time I’m trying to explain why.
If you need a photo editor, an advanced one, I suggest the wonderful photoline (it costs something like $50) or gimp which is free (and worse as many open source apps). On your wacom installation disk you may find adobe photo elements for free, Am I right?