[farshizzo]

You can use the undocumented vizdlg module to add the items within a panel. Here is a modified version of the script that uses the module:

import viz
import vizdlg
viz.go()

panel = vizdlg.Panel(layout=vizdlg.LAYOUT_VERT_LEFT,fontSize=25)
panel.setPosition(10,500,0)

def addSliderCheckbox():
	"""Create new row in panel containing slider and checkbox"""
	row = vizdlg.Panel(layout=vizdlg.LAYOUT_HORZ_CENTER,background=False,border=False)
	slider = row.addItem(viz.addSlider())
	checkbox = row.addItem(viz.addCheckbox())
	panel.addItem(row)
	return slider,checkbox

slider1,check1 = addSliderCheckbox()
check1.set(True)

slider2,check2 = addSliderCheckbox()
slider2.set(0.5)