I think you're better off using DataTemplate.Triggers
in this case rather than a Converter:
<DataTemplate>
<DockPanel>
<Image x:Name="Img" Height="16" Width="16" />
<TextBlock Text="{Binding Nick}" />
</DockPanel>
<DataTemplate.Triggers>
<DataTrigger Binding="{Binding Status}" Value="Active">
<Setter TargetName="Img" Property="Source" Value="{StaticResource ActiveIcon}"/>
</DataTrigger>
<DataTrigger Binding="{Binding Status}" Value="Idle">
<Setter TargetName="Img" Property="Source" Value="{StaticResource IdleIcon}"/>
</DataTrigger>
<!-- And So on... -->
</DataTemplate.Triggers>
</DataTemplate>