Well in ExtJS 3 i used the following code:
grid.getColumnModel().findColumnIndex("Tasks")
I tried finding it on the api docs, but no luck...so how is ir possible that i can find the column index of the grid by the dataIndex of the column or the header name of that column.
You can use the component query:
var fname = grid.down('[dataIndex=firstname]');
It took a while to work that out - there doesnt seem to be an example in the docs. ;-)