Got it working, very simple in the end (isn't it always?)
Just so anyone out there gets into the same predicament as your truly, here is how it works if you are using Currency Update 3.1 'curled' and happen to be using cpanel for your site's back end adjustments.
Go to 'cron jobs', select 'standard' (because it's the easiest way to go), enter an email address for the cronjob logs (not required, but useful to pin point problems, just set up an email address for it) and then type
"curl http://www.yoursite.com/locationofcurrencyupdatefile/currency_update.php"
Set a time for scheduling, as recommended here, once a day is sufficient.
Save the crontab and you are done.
Take care to leave the space between 'curl' and the full i.p address of where you have put the currency_update.php file. You can also leave the file itself as currency_update_curled.php and it shouldn't make any difference.
Make really sure that in the currency_update.php file your full paths are accurate, both for where the currency_update.php file is, where the store's root file is and the two files it needs access to. If you hit trouble, enter the FULL path for the two files, 'includes/configure.php' and 'includes/database_tables.php' like this...
// This describes the path from the location where you install this file to the root directory of your Zen Cart
// It is normally the only line that you will need to edit. See readme for guidance.
DEFINE('/home/username/public_html/whereyourfileis/','/home/username/public_html/zencart/');
/ Get Zen Cart configuration data
require_once('/home/username/public_html/zencart/includes/configure.php');
require_once('/home/username/public_html/zencart/includes/database_tables.php');
'Path' is just like the above, home/username/public_html/zencart/etc/etc.
Address is http://www.example.com/etc.php
A sucessful cronjob will return an email to you that looks something like this.
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
An unsucessful one will give you something else, but going with the above method seems to be nearly bulletproof, if only because I have tried dozens of other ways to get it working, and this is the only way that did it.
I hope that helps someone out there who gets stuck, and I wonder why a know nothing like me had to find out how simple it was after persuing all other methods...
