2007 Pivot Table - calculated field help

[ExcelUser123]

Hello All
I am having trouble inserting a calculated field. I am using a very simple pivot table, but I can't seem to figure it out.

Here is a screenshot:

Is there a simple way to incorporate this basic calculation into the table, so that I don't have to manually do it outside?
Thanks in advance for your advice

 

[ExcelUser123]

(edit) Actually looking for a percent of total

 

[ExcelUser123]

To further clarify, I am able to change the entire table values into percentages, but this would defeat the purpose.
Is there a way to display Grand Total and Percent of Total?

Thanks