I would like to rename a entry box label in the users section of admin. Could you advise me which file I need to edit to do this. I would like to change "Website".

i.e : zp-core/admin-users.php?page=users

The address fields come from the userAddressFields plugin.
In zp-core -> extensions -> userAddressFields.php line 50 change
gettext('Website') to gettext('whateveryouwant').

Note that with every update you will have to apply this change again unless you create a new plugin based on this one.
http://www.zenphoto.org/news/zenphoto-plugin-architecture

Thank you , but where would it be in version 1.4.3.3 as this differs to the current version ?

Not sure but try changing:
zp-core -> functions.php line 399

I hope you understand that we can't really support versions that old anymore.

Totally understand, just don't want to upgrade at this time. Thank you.