Download requires registering yourself to the site which I don't think anyone here will do.
But in the download link they clearly mention the installation procedure -
The trial version download is a ZIP file that contains a .Net 1.1 compiled version of strongly named assembly Winista.PrintLib.dll. Unzip the file in a folder. And then add reference to this assembly in your project where you want to use it. The namespace for the assembly is Winista.Reporting.Printing