Have you seen the Word Add-In Walkthrough document?
If you want to display different tables depending on the value of an xml tag, the easiest approach is to put each table inside a rich text content control, and add an appropriate condition to the content control.
If the value of your XML tag is literal 'true' or 'false' (ie you will have 2 tables), then the condition's XPath can simply point to the node.
If it will have other values (eg 'red', 'green', 'blue'), then your XPath will have to test whether the value is what you want (the expression must evaluate to true or false).
For the contents of the conditional content control to be inserted, the condition must evaluate to true.
The invoice document sample has a condition in it.
cheers .. Jason