What you are describing is often called a "cross tab" report. Not the easiest thing to set up but it can be done in FileMaker and the small scope of this particular chart makes this one fairly easy to setup. I'm assuming that you have FileMaker 11 or newer for this suggested solution to work:
I'll name your current table "RiskAssmnt" just to have a name to work with here:
Define a single summary field as the Total of Score in RiskAssmnt.
Define a self join relationship.
In Manage | Database | relationships, make a new table occurrence of RiskAssmnt by clicking it and then clicking the duplicate button (2 green plus signs). You can double click the new occurrence box to get a dialog to appear where you can rename the new occurrence box to be RiskAssmntByProb.
We have not duplicated a table. Instead, this is a new reference to the same table already present in your database.
Add it to your relationships like this:
RiskAssmnt::Probability = RiskAssmntByProb::Probability
Create a List View layout based on RiskAssmnt.
Remove the body layout part and replace it with a sub summary layout part specifying "when sorted by probability".
Put a portal to RiskAssmntByProb
Give it this Portal Filter Expression:
RiskAssmntByProb::Impact = 1
Select your summary field as the sole field in this portal and specify a one row portal (Initial row: 1, number of rows: 1).
Use copy and paste or ctrl/option-Drag to make 4 more copies of this one row portal. Double click each copy to open Portal Setup... and change the portal filter expression to:
RiskAssmntByProb::Impact = 2
RiskAssmntByProb::Impact = 3
and so forth.
When viewing your records on this layout be sure to sort them by Probabiltyor this layout will appear blank.
Thanks for your speedy reply. I will try this and let you know of the results.