Actually, you should have it but I'll bet it's where you didn't think to look.
1. Select your table or query to export.
2. Use the drop down in the dialog that appears to select the Text File (*.txt, *.csv,*.tab,*.asc)
3. Click the Export Button.
4. The Export Text Wizard should appear.
5. At the top, click Fixed Width (instead of Delimited) and then you can set your widths.
If you are doing this from code, you will need to do this once manually to create an Export specification that you can refer to in your code. Go here for a quick tutorial (screenshots) on how to create an export specification:
http://www.btabdevelopment.com/main/LinkClick.aspx?link=64&tabid=55&mid=385