Thanks, William, for the helpful advice, but I've been aware of an OS
restriction on number of files in a directory on Windows for some time.

I use httrack as part of a larger (automated) system, and beyond about 30K
files in a directory, the server system itself (.NET) runs out of resources,
without using Explorer. I presume it runs out of memory to store nodes in the
file structure (though I'm not sure of the internal details) and I've found
this documented elsewhere on the Internet. 

So I'm stuck between using the site-structure to store files, when the url
length can be a problem, or storing in a single directory when number of files
can be a problem. Hey-Ho.

Stevod