Old WinRAR versions stored supplementary files like a registration key, exported settings file settings.reg, themes or log file in the same folder as WinRAR executable. In Windows Vista and following Windows versions it is not recommended to store such data in the program folder. Software may even fail when trying to do it. Recommended locations for application data are subfolders of so called %APPDATA% folder.
Real path to %APPDATA% depends on Windows version. In English Windows XP installed on disk C: it is "C:\Documents and Settings\<user name>\Application Data", where <user name> is a name of user currently logged in. To open %APPDATA% folder do the following: run Windows Explorer or open "My Computer" window, type %APPDATA% in address bar and then press Enter. WinRAR stores its files in "WinRAR" subfolder of %APPDATA%. You may enter %APPDATA%\WinRAR in Windows Explorer address bar to go directly to WinRAR data folder.
Situations when you need to access %APPDATA%\WinRAR manually are rare. Samples of such situations may include copying settings.reg to another computer or browsing the error log file with some external viewer.
Note that WinRAR tries to search the registration key and settings.reg file both in %APPDATA%\WinRAR and in WinRAR program folder, with %APPDATA%\WinRAR having precedence.
If you need to override the location of %APPDATA%\WinRAR, you can set the string value "AppData" in Registry key HKEY_CURRENT_USER\Software\WinRAR\Paths containg a new path to WinRAR supplementary files.