HI Jerry -
What DWG viewer are you using? If you're opening a .dwg off of Constructware, you have the option to use the built-in Brava viewer, which doesn't require that you have any additional DWG viewer. It also allows you to redline, annotate, and measure the drawing.
Alternatively if you download the drawing, you can open it with any program on your computer, such as AutoCAD or DWG TrueView (http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=6703438).
Hope that helps - if you're still having problems, please call our support department at (800) 892-0449.
-Steve