I finally found the answer here: http://www.youtube.com/watch?v=8AxxcJ...
var v_rows = this.parent.numfieldname.rawValue;
// Replace FormName, PageName, TableName, RowName, etc. with the names for your form
You also have to make sure that
1) the fields under "Repeat Row for Each Data Item" on the Binding tab for the repeating row have been activated.
2) On File > Form Properties, Default tab, you select Dynamic XML Form on the PDF Render Format dropdown list.
3) On File > Form Properties, Preview tab, you have selected Dynamic XML Form on the Preview Adobe XML Form As dropdown list.