I would suggest making a customization to workitemedit.ascx that will update the comment field with the desired text.  Then possibly clearing the comment text when it gains focus so the desired text is not added to every incident.

A second suggestion, which I would not recommend would be to set a default value for the comment field of the workitem table in altiris_incidents.  

 w.current.workitem_comment = "Testing"

Here is actual code that will do the trick.  Place that in an appropriate place in the WorkItemEdit.ascx file and it will set your comment field to Testing.  Remember that when upgrading altiris its possible that your customizations are overwritten so creating a custom.config file and making a copy of WorkItemEdit.ascx in the custom directory would be better than just editing WorkItemEdit.ascx directly.

Hi Mccarthy,

I need your help,
I have customized the helpdesk and added the location field. Now I need that when users create a ticket, the location field should be selected.
Regards,
Rahiz

 mccarthy.cw's answer will do.
If you don't want to modify the code directly, you need to ensure that you are on HD SP5. Then you can use the Service Catalog and create a new Task in which the Comment field is pre-populated based on your needs.