Have you ever need to make some Marketplace 99×99 and 200×200 tiles for your WP7 App?
I had to made plenty of them – transparency is prohibited, so I made very simple and lightweight WP7 TilesCreator.
You can just move your any size transparent (or not) .png over the .exe file, and you obtaining two correct size files with red background.
Just look at screens:
I hope it is helpful!
Here is the application: