Hi BJ,
Change Tracking in Word does not exist in InfoPath. You can do SharePoint versioning on the XML files but this doesn't show you what changed. In fact, displaying what changed is the biggest hurdle.
You can record what changed by adding a separate ChangeHistory group node under your main data source's root node. Under that, add a repeating Change group node. Under that, add fields for FieldPath (xpath describing which field changed), BeforeValue (the value before it changed), AfterValue (the value after it changed), Date (date of change), Time (time of change), Actor (who did it). Next, you'll have to add an event handler on your root node and filter out changes happening under the ChangeHistory group. For all other events, you record the change info. You'll need code for this, but we could do it in an hour of help time if you need it. After you have this working, you need to find a good way to display the changes. This is the hard part. You can add a conditional formatting rule to all fields in your form and highlight them on load if there is a FieldPath in the Change group node that matches them. This requires code to query the Change group to find a node that matches. To show the BeforeData would require some kind of button to display previous. You could add a little hidden red calculated value near each field that only shows if the field was changed and shows the before value, but it will be difficult to make this look good in InfoPath's more table-oriented layout. Even Word looks bad after too many edits. Too bad you can't use the taskpane (not supported in browser). That would be a natural location to put the before-after values when someone selects the node.
Let us know if you want some paid support to implement this technique. I'm guessing 1-5 hours of work.
Best,