Alternative lenders reported generally good financial results last year. But making money wasn’t easy: some major players have had to make significant adjustments to their business strategies to keep their margins above water in a fiercely competitive environment. An example is Impac Mortgage Holdings, a real estate investment trust that reported $270.3 million in net income for 2005, up from $257.6 million a year earlier. Impac’s earnings increase was helped by a $144 million…