Hi John,
You should be using alias since names can be duplicate, but let's try it with name first and then you can change the dropdown to have name as the display and alias as the value. Here are some steps:
Add a data connection for GetMyInfo - see
http://www.infopathdev.com/forums/topic.asp?TOPIC_ID=848 for instructions. Replace "sAMAccountName" with "cn" so you can get the real name (cf. alias). Note: make sure that you leave the checkbox in the last dialog checked to call this on load). You don't have to set a value in your form, but for now, this simplifies things, so please add a value and set that node.
Add an On Load rule
1. In Designer, go to Tools->Form Options
2. Select Advanced
3. Select Open Rules
4. Create a Rule, called Check User
5. For condition, checks to see if the value in the field you added above against one of the names in the dropdown.
7. Add an action to switch to the read-write view
(assumes your default view is read only)
You can take the dropdown and add a secondary XML file and compare against the whole list on load using the User Roles dialog.
Sorry if this isn't clear, but I have to run. More later.