Well,
The expression would simply be:
ITF("000009910028")
This will return a barcode string. Highlite the variable, and apply the font PSMIntHrP72DmTt to it. That should make the barcode properly. That font is meant to be used in a size of 72.
If the number is in a field of your database, use this:
ITF([FieldName])
Where FieldName is the name of your field.
Hope this helps.
Regards,
Rapha