Select the chart, right click and select Chart Expert->Data and click on the field you have entered under "On Change Of." Then click on "Order" and choose specified order. Enter the names of the groups (and the criteria) as you would like them to appear on the pie chart.
Another method: With the chart NOT selected, insert a text box over the data label and enter the desired text. You will now have text overwriting text. Right click on the text box->Change Border and check "Background" and select white as the background (or the color of your choice). The color will block the underlying text.
-LB