Here's what you need to know about the Fed's surprise attack on the housing crisis.

And you thought 5 percent was a good rate? After already bringing mortgage rates down near 50-year lows, Fed Chief Ben Bernanke unleashed a surprise attack on the housing slump Wednesday by announcing aggressive steps that should make home loans even more attractive. Lower rates, of course, can help push timid buyers off the sidelines so they can mop up the excess inventory that's been driving down home prices. "This is a huge step forward," Ian Shepherdson of High Frequency Economics, wrote in a report shortly after the announcement.

Here's what you need to know about the development:

1. What is the Fed doing? With the federal funds target rate--which is the Fed's conventional monetary policy weapon--already down to as low as zero percent, Bernanke has been forced to get more creative in his efforts to resolve the economic mess. To that end, the Fed announced two key steps Wednesday that should drive mortgage rates lower.

2. Fannie Mae and Freddie Mac assets: The Fed unveiled plans to buy up to an additional $750 billion of mortgage-backed securities backed by government-controlled entities such as Fannie Mae and Freddie Mac, on top of the $500 billion it already committed to purchasing. At the same time, the agency said it would as much as double--to up to $200 billion--its purchase of Fannie and Freddie debt. The moves will help to reduce Fannie and Freddie's financing costs, which should enable them to pass savings on to consumers in the form of lower interest rates. Today's announcement represents a significant expansion of the initial initiative announced last fall, which drove mortgage rates from 6.2 percent in mid-November to 5.2 percent in the week ending March 13, according to HSH.com.

3. Long term Treasury bonds: Meanwhile, the Fed said it would buy up to $300 billion in long-term Treasury bonds over the next six months. The announcement has already helped push yields on 10-year Treasury notes--which play a key role in mortgage rates--down sharply. This could also help lower mortgage rates.

4. How low will mortgage rates go? Nigel Gault, chief U.S. economist for IHS Global Insight, says 30-year fixed mortgage rates could drop to as low as 4.5 percent. But Keith Gumbinger of HSH.com, expects a more modest decline of between a quarter and a half of a percentage point from current levels. "I don't think we are going to have a plummet, but I do think it helps to support some downward pressure on rates," Gumbinger says.

5. So what does this mean for the housing market as a whole? Before today's developments, lower mortgage rates have benefited those looking to refinance more so than home buyers, said Guy Cecala, the publisher of Inside Mortgage Finance, in an interview that took place before the announcement. Cecala said that in the fourth quarter of 2008, 51 percent of mortgage originations were for loan refinancing, while 49 percent went toward home purchases. And although it hasn't closed yet, "there is no question [the refinancing share of mortgage originations] is going to be up near 60 percent for the first quarter," Cecala said.

Today's Fed move should further boost refinancing activity. "It's a huge positive for refinancing, because it means that everyone who hasn't done it is going to come in and do it," Gault says. But its impact on the housing market will be less profound, says Richard Moody of Mission Residential. It will help "very little," he says. That's because "the overriding factor [in the housing slump] is the labor market, and consumer confidence," he says. Even with lower mortgage rates, housing won't rebound without improvement on these fronts--and Moody doesn't expect that to occur anytime soon. "You can't make the argument that mortgage rates have been the impediment to home sales over the past several months," he says.

6. How can I qualify for these low rates? As banks jack up their lending standards in the face of higher delinquencies, not all borrowers will be able to get their hands on today's lowest cost of financing. To do so, most home buyers will need to have a FICO score of roughly 720 or higher, a down payment of at least 3.5 percent--although it could be significantly higher in certain markets--and documented income verification. To refinance, borrowers will need to meet similar credit score and income documentation requirements and have minimum of 10 percent equity in their homes, Moody says.

7. What does that mean for me? Should I refinance now or hold off for a better rate? With rates poised to drop to even more attractive levels, fixed rate borrowers that meet the credit requirements should certainly consider refinancing now. (Refinancing, however, only make sense for borrowers who can obtain a large enough break in their interest rate to compensate for the fees associated with the process.) But since rates are expected to remain attractive for some time, there's no pressure to refinance immediately. Still, Moody points out that with home prices on the decline, borrowers who wait too long to refinance could find that they no longer have enough equity in their home to qualify. So you may be better off getting the process started sooner rather than later.

Likewise, homeowners with adjustable rate loans--who have likely seen their interest rate fall recently--should not feel compelled to act this very second. "There is not a gun to your head," Gumbinger says. However, borrowers with these products should keep close tabs on the market and look for an opportunity--perhaps now, perhaps in the coming months--to get into a more conservative, fixed-rate mortgage while rates remain low. "Do yourself a favor and prevent future disaster," Gumbinger says.