I hadn't found any example coding for how to access the REST XML API for Qualys in this community site, and I wanted to kick the tires on this API and see how it works. This Test GUI is very basic, but it would not be difficult to expand upon it or create a .Net service that makes these calls / etc.
If you don't have MS Visual Studio (C#) installed, you can get a free version here from Microsoft:
Once you have this installed, just unzip the QualysAPIV1TestGui.zip file and then open the QualysAPITestGui.sln file and press F5 to run it.
Once running, supply your Qualys ID, Password, and proxy server URL (assuming you have one to deal with).
From there, press the Call Qualys button as is to do a very basic test.
If that works out well for you, then try the dropdown which will copy other API URL's into the URL text box. Simply replace the parameters and press 'Call Qualys' again.
Calls that work are shown as text (xml) and also rendered as XML in the browser control for handy browsing.
Calls that don't work send you to the text result tab and the error is displayed.