Last week, I actively engaged in answering newsgroups posts for Blend. Here are some features not supported for authroing in V1. However, if you create it manually by editing xaml yourself and then load the project in Blend, Blend should be able to handle it just fine. If it crashes, then please let us know and we will try to fix it before RTM.
To create a NavigationWindow. In an empty xaml file, paste the following and point the source to whichever xaml you want in your project, in the example below it is pointing to Page1.xaml.<NavigationWindow xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="NavigationWindow Sample" Source="Page1.xaml" />
Another simpler way to convert a Window to NavigatinWindow, is to replace the <Window> tags with <NavigationWindow> and wrap the child element of Window with <NavigationWindow.Content> tags.