why doesn't this .htaccess work?

My admin said mod_rewrite is installed on my Apache server, version 1.3.27.

I have in tried several variations of the .htaccess contents to see if any
of them work, none have. Tried not specifying full path, specifying full
path,...

Here is what is in the .htaccess file:
ErrorDocument 404 index.htm

I put this under directoryA so that all page requests for missing files go
to index.htm

The index.htm is there.

When I try to pull up a file that IS NOT on the server, it displays this:
"Not Found
The requested URL /dfpo/jj/index.htm was not found on this server.
Apache/1.3.27 Server at mysite.com Port 80"

Any ideas?