You can use MSDE, a SQL server compatible database engine that MS makes available for free. You can download and install MSDE from a whole variety of sources. Here is one source.
MSDE also comes with Visual Studio.NET / .NET framework SDK. It is available under $(VS Install drive):\Program Files\Microsoft Visual Studio .NET\FrameworkSDK\Samples\Setup\msde. You can then run $(VS Install drive):\Program Files\Microsoft Visual Studio .NET\FrameworkSDK\Samples\Setup\configsamples.exe to configure the northwind database that the samples use.