The complete FAQ is here: http://lab.msdn.microsoft.com/express/faq/default.aspx
In a nutshell though, the Visual C++ Express Edition product is a perfect tool for those of you developing DirectX applications at home. It contains the full optimizing C++ compiler, plus powerful features like Intellisense. The Express products are currently free to download. We've also created the Express products to be 50mb in size or less, making the download relatively painless for those of you on a broadband connection.
I encourage you to check out the Visual C++ Express Edition Beta today!