Vista - WPF Layout(?) Question

I am trying to design a WPF layout with placeholders for certain visual
elements. These will be loaded at runtime.

For example, I have a tab control which is going to display a
panel(DockPanel? StackPanel?) which contains a number of other controls
(drop-down boxes, option buttons, etc).

I am looking for examples of how to do this (assuming the explanation
makes sense). I'm very new to all of this, and I don't know if I should
create another window, xaml page, or a custom control. For anyone
familiar with Java Struts, the approach is very similar.

I tried manually creating a xaml page, which contained the markup for a
DockPanel, which contained a button. I tried to load this into my tab
control using Resouces, but it didn't work. I need a simple example.

Does what I am trying to do make sense? Is there a better way of doing
this?

Any help would be very much appreciated.

Thanks!