Prioritizing Tasks

[Don Green]

I use MS Outlook from MS Office 2010, with Windows 7 Pro.
The specific version of Outlook I'm using is shown as 14.0.4760.1000.

On my task list, I'd like to prioritize tasks numerically from 1 to
20. The only priority I see is "Low", "Medium" or "High".
I added the column Custom Priority, but it won't let me write anything
in that column.

Is there a way to prioritize on a more granular level than just Low
Medium or High?
If so, how?

Thanks!