The Subversion help describes the "export" command as follows:

export: Create an unversioned copy of a tree.
usage: 1. export [-r REV] URL[@PEGREV] [PATH]
       2. export [-r REV] PATH1[@PEGREV] [PATH2]

I mistakenly assumed that URL or PATH1 was required before the first path parameter. Alas, this is not the case and it took me a while to work out what I was doing wrong.

To export the HEAD of a path from the repository to a path on the C: drive you would use something like the following:

svn export svn://server/path c:\path –username stu
–password pwd –force

To export from the working copy to a path on the C: drive you would use something like the following:

svn export c:\workingcopy\path c:\path –username stu
–password pwd –force

Simple really. A bit like me.