Open the windows start menu -> execute and type in:
wordpad

This will start the WordPad. But how does this work?
Some Applications are registered in the Registry.
e.g.: dialer, WinWord, Excel, mplayer, Winzip, ....

uses Registry, RegStr;

function TrueExecutablePath(const path:string):string;
var
   Reg: TRegistry;
begin
   result := path;
   if not FileExists(path) then
   begin

      Reg := TRegistry.Create;
      try
         Reg.RootKey := HKEY_LOCAL_MACHINE;
         Reg.Access := KEY_READ;
         if Reg.OpenKey(REGSTR_PATH_APPPATHS+'\'+path, False) or
            Reg.OpenKey(REGSTR_PATH_APPPATHS+'\'+path+'.exe',False)  then
            result := Reg.ReadString('')

      finally
         Reg.CloseKey;
         Reg.Free;
      end;
   end;
end;

see also article 1007.

please drop me a mail, if there is a shell function,
with scans the search paths too. (there must be one,
because the shell searches the registry and the search paths)