Pre-qualified isn't worth the paper it's written on. It means nothing. Nobody will take you seriously. Make sure you get pre-approved from your lender and that it says so in writing! Some lenders and Realtors will tell you it is the same thing. It is NOT.
The key difference is that for a pre-approval, you have to give permission (in writing usually) for the lender to look at your credit report and score. They make require pay stubs or tax returns too. For pre-qualification, the lender takes your word for income, debts, etc.
Pre-quailified means they take your word as to what you make, what you owe and may look at a soft copy of your credit. To be preapproved they get all your financials, bank statements, tax retruns and verify them as well as your job. Anyone can get prequailified but only the quailified will get the pre-approval.