Add CountIF Function to Formula Dialog

[owp^3]

I need to be able to Count Tasks conditionally and see the results in PWA
Project Center views.

There is a Task Count formula but it counts all the tasks in a file. I need
to be able to count just the milestones and then just the milestones that are
past due.

I'd like to add a Function to the Functions Menu in the Formula Dialog box.

Would this be fairly simple or would it take a lot of development?

Is there a better approach?

Thanks,