How to get column index when click on header ?

Is it posible to get the index on the clicked column header?

The reason why is that i want to make an own sort and then get a new subset of data from the server. (Easier to sort more than 25 000 rows in the db)

I have tried to call a function (myFunction) that takes the index as as a parameter . The question is how get the index???

var header = new Active.Templates.Header;
header.setEvent("onmousedown",myFunction(HowGetTheColumnIndex));
obj.setTemplate("top/item", header);