I believe the name of the current form is stored in the this.Uri property (there should be no difference between FormServer or regular InfoPath).
Hence, the code would look like this:
this.MainDataSource.CreateNavigator().SelectSingleNode( "/my:myFields/my:field1", this.NamespaceManager).SetValue(this.Uri);
"/my:myFields/my:field1", this.NamespaceManager).SetValue(this.Uri);
Where "/my:myFields/my:field1" is the xpath to the field you want to set.
Hope that helps,
David.
David Airapetyan / Software Services ArchitectQdabra® Software / Streamline data gathering to turn process into knowledge