Pre-Qualified vs. Pre-Approved
Getting pre-qualified just means that you have told a lender your income level and your debt and credit information, and the lender has estimated what you can afford.
Pre-approval, however, puts you much closer to the actual loan and means that the lender has done the legwork of pulling your credit report, checking your debt-to-income ratio, and has done a more in-depth analysis of your financial situation. In most cases, you're much better off getting pre-approved so you don't have any surprises when a lender checks your credit report -- particularly if you haven't checked the report yourself first.