Hi Wayne

I understand you can do it like this.

first define a resource with a name and type material

in the resource information, fill all details of this material resource with the "fixed cost" you have in mind

on the task information window

assign this material resource to the tasks required and classify as "cost by Use "

it now should show as a fixed cost.

What a great question....  we need to make that more apparent.  Here is another way you can do this

1) in the Spreadsheet pane on the Gannt Chart in the top left hand corner between Name and the Task number is a box..... click on the box and you will see a set of options.  This is the collumns that can be shown on the Gantt Chart.  You might want a cost view in the spreadsheet for instance.  So select cost

2) You will see the spreadsheet columns change.  If you scroll over you will see a column for Fixed Cost. You can enter a value.

3) You can also add a column to any of the preconfigured spreadsheet layouts so if this is common you can just add Fixed Cost as a column to the default spreadsheet layout..