The technique you're attempting to use is referred to as "indexed properties". If you check out question 6 of the JavaRanch Struts FAQ you'll find a lot of good information about this topic, as well as a working example.
Regarding your example, you're almost there. Just change your JSP as follows:
The trick is that the id of your logic:iterate must have the same name as your indexed property, which in this case is customers.
Also, the setter in your ActionForm must be changed. It should look like this:
[ July 23, 2007: Message edited by: Merrill Higginson ]