If when composing or editing a label style, you happen to notice that your preview window is blank, this may lead you to believe that there is a graphics card issue or possible corrupted installation. Typically this issue has nothing to do with either of those, but rather the naming (or renaming for that matter) of this folder:
Windows XP: C:\Documents and Settings\All Users\Application Data\Autodesk\C3D 2012\enu\Data\Preview
Windows Vista & Windows 7: C:\ProgramData\Autodesk\C3D 2012\enu\Data\Preview
These previews are stored as .DWG within these subfolders, so renaming them or any changes to the folder structure will cause the program to display a blank preview window. This is actually documented in the HELP menu within Civil 3D, but given the misleading nature of this issue it could lead down the wrong troubleshooting path. Enjoy!