Application Data\DPlot folder
On Windows 2000 and XP, this is a hidden folder under c:\Documents and Settings\<username>. 'Application Data' may be spelled differently, depending on your language settings. On Windows Vista and newer versions of Windows this is a folder below c:\Users\<username>. You can access the Application Data folder with the shortcut %APPDATA%.
On previous versions of Windows the referenced file may be found in the folder where DPlot is installed. If you used the default installation path of the setup program this is c:\Program Files\DPlot.