Vista - autocomplete in a Textbox possible?

In windows forms it had been so easy, in WPF/XAML I just can't find it:

how do I enable some kind of autocomplete for a Textbox?

thanks,
Sam

I think autocomplete is implementable without changes to any logical tree,
so there wouldn't necessarily need to be explicit support for that
functionality. Basically, if you hide a dropdown list under your textbox's
controltemplate & trigger it to turn on when the text changes, you should
just have to bind the contents to a datasource of your choice (what is your
autocomplate control completing?), with the current contents of the source
textbox as the filter.