Have you considered extension objects in v10 for a Gantt. If you have done a full install of QV10, then in folder C:\Program Files\QlikView_10IR\Examples\Extensions, double-click on the Gantt.qar file.
Then close/re-open v10 and in the start page you should see extension examples as a sample file, just under DataVisualizations. Might be helpful.
Also followed John's example and got it working. Now I found that this Gantt Extension only works when I set the date format in the load script to 'MM/DD/YYYY' and not my default 'DD-MM-YYYY' as used in the Netherlands. And this causes me for any date-field displayed to use date formatting on field-level. Any ideas here?
Another question with this extension...
Is it possible to have influence on the scaling? For instance group by quarters instead of months?
Finally I found this extension to have quite a negative impact on the overall performance?!