SQL Server 2008 is available in numerous editions, and the features available to you in each edition vary widely. The editions you can install on your workstation or server also vary based on the operating system. The editions of SQL Server range from SQL Express on the lowest end to Enterprise Edition on the highest. The prices of these also vary widely, from free to more than $20,000 per processor.
Ted Kummert, Microsoft corporate vice president, announced at the Professional Association for SQL Server (PASS) conference in September, 2007, that prices for SQL Server 2008 would remain the same as they were for SQL 2005. No price increase—woohooo!
SQL Compact is a free edition which is intended to be an embedded database for mobile and other compact devices with occasionally connected users.
SQL Express is the free version of SQL Server meant for installation on laptops or desktops to support distributed applications such as a remote sales force application. You can use this edition to store sales or inventory data for your disconnected sales force and replicate updated data to them when they become connected again. SQL Express was called Microsoft Desktop Edition (MSDE) in SQL Server 2000. It is extremely lightweight and does not occupy much hard drive space. Vendors are free to distribute SQL Express, and it can be wrapped into your application's installation as just another component. ...