To create a custom landing page to your store, create your own custom HTML page using the editor of your choice, and save the file as "default.htm" (no quotes).
After you've created your landing page, connect to your account via FTP, and upload the file to your "/web" folder.
Once this is done, anyone visiting your site will see your customized landing page rather than your store's homepage. This will also cause all "breadcrumb" links and any links pointing to "Home.asp" to direct visitors to your custom landing page.