I know the OP was asking about doing the export from the command line, but just in case this is helpful to anyone else out there...
You could just let Eclipse (plus one of the plugins discussed here) do the work for you.
Obviously, downloading Eclipse just for doing a single export is overkill, but if you are already using it for development, you can also do an svn export simply from your IDE's context menu when browsing an SVN repository.
Advantages:
- easier for those not so familiar with using SVN at the command-line level (but you can learn about what happens at the command-line level by looking at the SVN console with a range of commands)
- you'd already have your SVN details set up and wouldn't have to worry about authenticating, etc.
- you don't have to worry about mistyping the URL, or remembering the order of parameters
- you can specify in a dialog which directory you'd like to export to
- you can specify in a dialog whether you'd like to export from TRUNK/HEAD or use a specific revision