I'm assuming this "top level  site" is a team site  with a URL like
http://server/sites/thesite ? If so, you can use the WSS backup  utilities.
spbackup will backup everything including permissions, but it will do the entire
site collection (e.g., the site and all it's subsites). smigrate can backup
just the site without the subsites, but it will likely lose the site members and
permissions settings.

Yes, I just want to backup  the site, i.e., http://serer/sites/thesite.

Where can I find the WSS backup utilities that you mentioned below?

I don't remember the exact path, but if you search your server for
"smigrate.exe" you'll find them all in the same directory. The administrator
documentation has information on using them.