Steps to do
1. Create a type "MainWindow" that inherits Window()

__namespace FSTest
__type MyWindow()
____inherits Window()

____member this.xx="myMember"
____....
____....

2. RootElement of the "MainWindow"Xaml-Ressource has to be type of your "MainWindow"
__Add Namespace of your Project to XAML-file
__Set Type for Xaml-RootElement
__
___(f:MyWindow
_______xmlns:ms="[link:namespaces.mindscape.co.nz]
_______xmlns="[link:schemas.microsoft.com]
_______xmlns:x="[link:schemas.microsoft.com]
_______xmlns:f="clr-FSTest;assembly=FSTest" // f := Namespace and AssemblyName of yor Project
_______
_______ (Window.Resources)
_______ (/Window.Resources)
_______ (Grid)
_______ (\Grid)
_______.....
_______.....
___(\f:MyWindow

3. Create EntryPoint and main-Method in a Module
__
___namespace FSTest
___module MyApplication=
___[<EntryPoint;STAThread>]

___let main (args:string[]) =
_____let startUri=new Uri("MyWindow.Xaml",UriKind.Relative)
_____let app=new Application(StartupUri=startUri)
_____let result=app.Run()
_____result

4. Go on with XAML-File, Define the EventHandlers for Controls, Commands and EventSetters
__
_____(Button Content="Cilckme" Click="ButtonClick" )(/Button>)
_____....
_____....

5.Write Code behind for the delegate-Methods in your "MainWindow" type
__
__namespace FSTest
__type MyWindow()
____inherits Window()

____member this.ButtonClick (s:obj) (e:RoutedEventArgs) =
________let sender=s :?> Button
________let MessageBox.Show(sender.Content.ToString())
________()

6. Debugg, enjoy it

In the attached you can find the a samle of my FSTest.
It would be fine if someone could help me by making a "F#-WPF-Xaml" Template for this Project.
I like F#, it's great