How to do a iteration of a set of elements in a test request xml using SoapUIPRO

Actually I think you would have a problem with looping within the request itself (it doesn't seem to like embedded curly braces {})

I would do it externally in a DataGen step, or as an XQuery Property Transfer.

Here's an example for XQuery : http://www.eviware.com/index.php?option=com_content&task=view&id=84&Itemid=44