Microsoft is in talks to buy CrowdStar, a company that makes games for Facebook. CrowdStar’s biggest game is Happy Aquarium, which boasts more than 26 million active monthly users.

Bloomberg’s sources say that Happy Aquarium is valued at $200 million. That might seem ridiculous, but when you consider that Electronic Arts acquired Playfish last year for $400 million, it just might be true.

CrowdStar is apparently the fourth-largest Facebook developer, so nabbing the company might be very much in Microsoft’s interest — if it does in fact want to enter the social game space. It’s unclear if CrowdStar’s games would be ported over to the MSN Games portal that Microsoft currently runs, or if the games would be added to Xbox Live.

In any event, the huge success of FarmVille and its estimated $1 billion valuation underscores the enormous potential of this sector, especially in the area of virtual goods.

The games themselves are free and relatively inexpensive to produce — but users are addicted and are more than willing to spend money on virtual goods. Microsoft already has a virtual goods ecosystem and community built around Xbox Live. If it could pair that experience with some of the most popular social games — whether by CrowdStar or someone else — the platform as a whole could become compelling in an entirely new way.

Tags: CrowdStar, happy aquarium, social gaming, Zynga