Hi Ben
Thanks so much for the quick response. I'm trying to puzzle my way around the screens, but it's getting late here in the UK, so I'll pick it up again tomorrow. Just to give you an idea in the meantime, I have created custom versions of CRM_LeadList and CRM_EditLead, both of which have been set up to replace the links from the original screens. The Search button is set to show a custom version of CRM_Search_CustomerList in the pop up.
Clicking on Go To.. directly from the custom Leads and Contacts List opens the custom Edit Lead screen fine, and Go Back works too. It's just the Search bit that won't work.
Best wishes
Francesca