Microsoft released a Fishbowl which is a Silverlight based Facebook desktop client.
This is a cool application which will help you to use the facebook more easily. Brag and drop photos will upload the photos to Facebook and share.
Mini-mode offers an unobtrusive way to stay connected.
The full mode
Operating system: Windows XP with Service Pack 2 (32-bit edition only), Windows Vista (32-bit or 64-bit editions), Windows 7 (32-bit or 64-bit editions), or Windows Server 2008.
Processor: 1 GHz or higher for Windows 7 or Windows Vista; 800 MHz or higher for Windows XP.
Memory: 1 GB of RAM for Windows 7 or Windows Vista; 512 MB for Windows XP.
Internet connection: Internet functionality requires dial-up or broadband Internet access (provided separately). Local or long-distance charges may apply.
Graphics or video card: A video card that supports DirectX 9.0 or higher, and Shader Model 2.0 or higher.
Read this too from Microsoft
Fishbowl is a trial application and a sample demonstrating a unique user experience with Facebook content, optimized for Windows 7. It is available for download by technology enthusiasts and Facebook power users. Since it’s currently a trial version, we don’t support it. But don’t let that stop you from kicking the tires (and from sending us your feedback)!