Hi Nate,
I have entered a test user, and had a look at the table:
The windows user name is not there, only the Windows Security ID. As far as I know, the page fields are validated in the display order of the page. Question: did you just publish the User Card or have you created your own page? I would suggest to create your own page.
If all this is too cumbersome, the other way to go would be to create your own codeunit and xmlport for a webservice. I'm not sure which way I would go, after a few tries with the page I would say "then the other method". ;-)
with best regards
Jens