You can build your gallery online, but you can add it to your web site off line. Highslide uses its own styles and classes. The styles and classes you’re using in your web site shouldn’t affect the ones used by Highslide.
First go the Highslide Editor
and create your gallery with your own images (use the Image manager in the Gallery tab). There are several predefined setups in the General tab. Click the Publish button when you’re satisfied with your gallery. Accept the license conditions (click Yes). Choose “Download a zip archive” and unzip. Copy the highslide folder (found inside highslide-custom folder) to the root of your local web site. Open highslide-custom-example.htm in Expression Web. Go to Code view. Copy everything between <body> and </body> and paste it in your page where you want your gallery to appear. Also copy everything between </title> and </head> and place it right before </head> in your page.
You should now have a page with a working gallery ready to upload to your server. (You need to allow blocked content to view the gallery locally in IE.)