Hi there. From your post, it sounds like you are interested in determining the size of an array in a cluster and accessing other elements of the cluster. In LabVIEW, this can be done by unbundling the cluster and/or using property nodes for the different elements in the cluster. Property nodes are created by right clicking on an element and selecting Create>>Property Node, which opens up a list of properties you can view or change.
If this doesn't answer your question, please describe what exactly you are wanting to do. Also, this may have more responses if you post on the LabVIEW forum.
Hope that helps!
Lorielle P.
Applications Engineer
National Instruments