[PhoeniX]

Элементарно, Ватсон:

Код:

function ShortFileName(const FileName: string): string;
var
  aTmp: array[0..255] of Char;
begin
 if GetShortPathName(PChar(FileName), aTmp, Sizeof(aTmp)) = 0 then begin
      Result:= FileName;
   end
   else begin
      Result:= StrPas (aTmp);
   end;
end;