наибанальное...
Код:
function TForm1.CheckStr(sstr: string): boolean;
var
i: integer;
begin
CheckStr:=false;
for i:=1 to length(sstr) do
begin
if (copy(sstr, i, 1)[i] in ['a'..'z']) or (copy(sstr, i, 1)[i] in ['A'..'Z']) or (copy(sstr, i, 1)[i] in ['А'..'Я']) or (copy(sstr, i, 1)[i] in ['а'..'я']) then CheckStr:=true;
end;
end;