If that does not work you can use the API. There is an API call on the Workspace that gets all content changes since a given point in time:
findContentModifiedSince
public com.ibm.workplace.wcm.api.DocumentIdIterator findContentModifiedSince(java.util.Date modifiedDate)
Returns an iterator of IDs of all Content that have been modified since the specified date. The IDs returned will include those for Content that have been modified on the given date. If no content has been modified since this date, or the user has access to no documents in this set, then the iterator will not return any elements. null will never be returned.
Parameters:
modifiedDate - the date with which to compare Content last modified date
Returns:
an iterator over objects modified since the given date that are visibile to the current user
...or if you have 6.0.1.3 there is some new API stuff that you can tie to workflow. There is a nice article on developerWorks on that concept.
Michael Fromin
Ephox
http://www.ephox.com/ibm