Here is an example of what you can do with .NET. All components of the server and client are written in C# .NET with a MySQL database. The server uses .NET Web Services which normally run through IIS, but it this case have been made to work on Linux thru MOD_MONO. The whole project is open source and worth taking a look for a couple reasons. #1 Pure exposure to client/server/database architecture. #2 Exposure to performant code (not that the architecture is the fastest it can be, but that sets a good example of realtime speed).

* New Release version 1.29 * http://sourceforge.net/project/showfiles.php?group_id=101941&package_id=139445&release_id=306774

The most notable changes are:
* Major performance updates
* All aspects of the model are now collaborative (vertexes, colors and textures) -- Any change you do, you'll friends will see
* You can now import textures from a file into the scene (supports BMP,JPG,PNG)
* The server is now running on Linux with Apache/Mod Mono/XSP which was changed from originally using Windows/IIS

http://www.tagcma.com/images/articles/20050220014654353_1.jpg