See solution in other versions of Excel:
Question: How do I insert a new column in Microsoft Excel 2007?
Answer: Select a cell to the right of where you wish to insert the new column.
Right-click and select "Insert" from the popup menu.
When the Insert window appears, click on the "Entire column" selection and click on the OK button.
A new column should now be inserted to the left of your current position in the sheet.