Todd mentions ways to make files available to tests or at runtime in VS. If you happen to be using MS Test, you have one more option that I don't believe was mentioned, the DeploymentItemAttribute. From the MSDN page:
This attribute can be specified on a test class. There can be multiple instances of this attribute to specify more than one item. The item path can be absolute or relative. Relative paths are relative to the RelativePathRoot setting found in the .testrunconfig file.
The following examples demonstrate different usage of the DeploymentItemAttribute:
[DeploymentItem("file1.xml")] Deploys an item named file1.xml located at the RelativeRootPath. The file is deployed to the deployment root directory.
[DeploymentItem("file2.xml", "DataFiles")] Deploys an item named file2.xml located at the RelativeRootPath. The file is deployed to the DataFiles subdirectory of the deployment root directory.
[DeploymentItem("C:\\MyDataFiles\\")] Deploys all items and directories found within the MyDataFiles directory. This does not create the MyDataFiles directory underneath the deployment directory. All files and directories within MyDataFiles will be deployed to the deployment root directory. To copy the entire MyDataFiles directory structure, you must specify MyDataFiles as an output directory.
Of course, the truth of the matter is that I would rather use MBUnit :)