In InfoPath 2010, when adding a form field to be available as a column on the SharePoint form library (File >> Advanced Form Options >> Property Promotion >> Add), the option to make the field editable from the library is missing. Instead of a checkbox with the message “Allow users to edit data in this field by using a datasheet or properties page”, there is a message “Some options are hidden when publishing to SharePoint Portal Server 2003.”
The solution is pretty simple. Re-publish the form (File >> Publish >> SharePoint Server (Publish form to a SharePoint library). Do not use Quick Publish!). As you go through the Publishing wizard, keep the selections the same to update your published file. The fourth screen will look identical to the Property Promotion dialog, but when you click Add (or Modify), the option to “Allow users to edit data in this field by using a datasheet or properties page” will be there.