When it comes to casual games online, they tend to be built in Adobe’s Flash (see Kongregate). But Microsoft wants people to start creating Web video games in its competing Silverlight.

Today, it is taking a step to make that easier by introducing the Popfly Game Creator. Microsoft launched Popfly last year as an easy way to create widgets and mashups using Silverlight. With Popfly Game Creator, it is adding a simple Web-based authoring environment for creating casual arcade-style games.

The tool is built for non-programmers so that anyone can create a game, and is particularly aimed at kids and teenagers. It is entirely browser-based. You create a game using predefined templates that can be modified, and when you are satisfied, you hit play to run the code. The games run in Silverlight and will be hosted at Popfly, but are embeddable anywhere on the Web. Here’s a game Microsoft created for us with Michael as the main character.

The Game Creator starts off with templates for about 20 different types of games—from space invaders and breakout to racing games and shooters. Game makers can populate their games with hundreds of characters, background scenes, sound effects and objects, or create their own from scratch. More details can be found on the Popfly wiki.