To download the code, you must have an SVN tool. The D2BS team uses TortoiseSVN, which is a very nice SVN tool that integrates directly into the windows shell.
To compile D2BS, you must have Visual Studio 2008 or Visual C++ 2008 Express. If you use the Express version, you must have the Windows Vista SDK installed. You can find the necessary software to compile D2BS here and here.
The only necessary options in the SDK that you must install are under the Developer Tools --> Windows Vista Headers and Libraries category. You must select Header files and x86 Libraries. Everything else is unnecessary, though you may also want the debugging tools.