CNNMoney reports that new rules proposed by federal regulators last week are intended to discourage risky investments, but will likely make credit even tighter.  On home loans where banks receive less than 20 percent down payment, they will be required to keep five percent of the loans instead of selling them as securities.  The end result could be that banks will not make loans where less than 20 percent is put down, adding weariness to an already wearied housing market.