- Host: sites.google.com
- Domain: [leave blank]
- Webspace: [the last part of domain name path; if the domain name is http://sites.google.com/site/mysite123, this value would be just mysite123]
- Import/Export Revisions: [I left this unchecked]
- Username: [my Google account, with @gmail.com at the end]
- Password: [the obvious]
- Choose Target Directory: [the obvious]
Here's Google's blog post that talks about the issue a bit more.