You are going to need to use the following
xml code:
<Window>
<Position>
<Resizable Allowed="Verticle">
<MinWidth>50</MinWidth>
<MinHeight>50</MinHeight>
</Resizable>
</Position>
</Window>
Obviously some fields are left out but you get the idea... note that all the above information is avabile in the scripting documentation you can download...
As for the other question yes you can you just need to initially set the width to stretch then use an anchor on the left and right and bottom.