It seemed like a good idea at the time. Just a few years back, when housing prices were soaring and interest rates were at historic lows, millions of Americans grabbed adjustable rate mortgages with super bargain basement rates. For many, it was the only way to jump on the American housing train.Now that train is slowing, big-time. Home sales and prices are slumping in many markets. Interest rates are up and so are foreclosures, as the first big wave of adjustable rate mortgage holders face the music: sharply higher monthly payments or a scramble to refinance and push out the pain as housing prices stall.