I am in favor of fixed-rate, amortized 30-year loans because you know what you will pay. Adjustable-rate loans (typically called ARMs) make me nervous because the rates are likely to go up over time. Watch out for "teaser" rates that expire in few months, because you'll be paying much higher rates later. Avoid negative amortization because you will end up owing more than you borrowed. Generally, you'll get the best rates if you have a high FICO score and can put 20% down. But there are first-time homebuyer programs that offer below-market interest rates and help you with the downpayment.
My favorite mortgage calculator is at the New York Times -
http://homefinance.nytimes.com/nyt/mortgageCalcs/calculator/mortgage
While this gives you an idea of monthly mortgage costs, don't forget to add about 1.5% for property taxes and .3% for home insurance. You'll have HOA costs if you move into a condo or TIC. You should also put aside money for repairs and improvements. Your lender will probably require you have enough money set aside to pay several payments.
It has gotten harder to get a loan than it was just a year ago. But that's not necessarily a bad thing, because you want to keep the home you're buying, not lose it to foreclosure. Lenders seek a consistent earning history, regular debt payments, and a debt-to-income ratio of below 45%. In other words, they want to be sure that you can make the payments. I can give you some basic pointers on fixing your credit, and my lender can give you additional suggestions.
