You can make a Web site viewable offline without any additional software. All you need is a browser (MS Internet Explorer, Netscape, Opera, etc.) When you finish downloading a site to your hard disk, please select the corresponding Project, click the Export button on the Ribbon - Home tab and export the site to the disk on your USB drive (For example, disk G:\).
Please make sure you check the "Use Standard extensions for files with known file types" box before you start exporting. You can also check the "Make AutoRun CD" box. If the system supports autorun on the USB drive, the site will be automatically opened.
If autorun will not work on the USB drive, you will be able to open the contents.htm file on the USB drive to start browsing the site. On most systems it is enough to double-click contents.htm in Windows Explorer when you view the USB drive contents.
You can read more about the Export feature here.