Loading AJAX dataset: no "processing" state, only "No data available in table"

I have this in my table definition:

oLanguage:      { sProcessing: "<img src='../images/spinner2.gif'>" },

But whilst the table is gathering data from AJAX (which displays fine, after about three seconds) there is no indication of life, only of an empty table ("No data available in table") which is a little disconcerting.

Can I force it to show it's processing state on initial load?

Thanks!

Iain