It wouldn't be unless you reference the dll - System.Windows.Forms.dll.
Huh? You just need to referece System.Windows.Forms.dll. You can use
Windows forms controls inside of a WPF app, so you most definately can
reference the dll. You just have to add the reference manually.
Of course, since this is a wpf app, using Application.DoEvents is
probably not the right solution anyway...
You might want to look here for a wpf implementation:
The code is C#, but, it should be a fairly simple conversion (the code
is not very complex).
I wonder if you can get your blink effect without using a sleep... Have
you tried looking at the wpf animation support?