i created a UserMulti field inside my list's instance. Heres how i declared it.
<Row>
<Field Name ="Title">List1</Field>
<Field Name ="aatMessage">Message place holder</Field>
<Field Name ="aatStartDate">2012-03-01T09:39:44Z</Field>
<Field Name ="aatEndDate">2012-03-31T09:39:46Z</Field>
<Field Name ="aatColleague">DTM01\Mathieu.Landry</Field>
</Row>
The problem i have is filling up the "aatColleague" field. Adding my user doesnt seem to work. I tried without the DTM01 and it still doesnt work. Also since i added this, the item doesnt show in the list anymore but if i remove the aatColleague field it all works.