How to use DispatcherTimer?

I have a WPF application. I have a panel that I want to repopulate every 1 minute getting data from the network. I know that I can use the DispatcherTimer class to set the timespan for ticks and make my code execute in every 1 minute.
The problem here is the my GUI freezes and becomes unresponsive as my code is busy fetching data from the network. I can create thread and handle it concurrently like I would have ideally done it in Winforms world. I would like to know that is there any better way in WPF as this is a new World for me.

I am doing it like this:

DispatcherTimer

_timer = newDispatcherTimer();

_timer.Interval = TimeSpan.FromMilliseconds(1000);

_timer.Tick += newEventHandler(delegate(object s, EventArgs ev)

{

App.DefaultMainWindow.ContentBrowser.OverviewControl.CallLoadMessages();

App.DefaultMainWindow.ContentBrowser.MessagesControl.CallLoadMessages();

});

_timer.Start();

This code freezes my GUI. Please help.

Thanks,
Vishal