The Windows Preview Pane will display ".txt" files, but many others files are really text but have other extensions. For the slightly brave at heart, there's a fix for that, but it takes some changes to the Windows registry.
Open the registry editor (regedit.exe) and navigate to HKEY_CLASSES_ROOT\.ext, where ".ext" is the extension you want to add, such as ".bat" in the example below. Add two new string values of type REG_SZ named "Content Type" and "PerceivedType". Note that one of these has a space in the middle and the other does not. Set the value of Content Type to "text/plain" and PerceivedType to "text'.