To change the width of stacked columns in Excel 2007, you can follow these steps:

1. Select the stacked column chart that you want to modify.
2. Click on the "Format" tab in the ribbon.
3. In the "Current Selection" group, click on the drop-down arrow and select "Series".
4. Click on the "Format Selection" button.
5. In the "Format Data Series" dialog box, go to the "Series Options" tab.
6. Adjust the
   Formula:

   "Gap Width" 

   slider to increase or decrease the width of the columns. You can preview the changes in the chart preview area.
7. Click "OK" to apply the changes.

If the columns still appear as thin coloured lines after adjusting the gap width, you may need to adjust the chart's scaling. To do this, right-click on the chart and select "Format Chart Area". In the "Format Chart Area" dialog box, go to the "Axes" tab and adjust the scaling as needed. This should make the columns appear as normal size coloured vertical bars.