I must be overlooking something completely obvious.  I'm trying to make
certain fields on a form that can only be changed by certain users.
Can this be done using Roles?

First I created a User Role called HR with the HR user's Windows
username in it under User Assignments.

Then I tried to apply rules and/or data validation to particular text
fields on the form.

I've used the condition "User's current role" and "is equal to" and
"HR".  (I also tried "is not equal to".)  Regardless of what variation
I try, any user (or none) is able to change data on in this text box.

InfoPath does not seem to properly detect what user is logged in to
Windows using the form -- is InfoPath supposed to even do that or do I
have the whole idea of roles and users confused?