Some practical advice from a recent home buyer (7/2004):
1. Use sites like bankrate.com that have mortgage calculators to get an idea how much house you can afford. Remember that beyond the principal and interest you need to add in home insurance, property taxes, PMI,  and other miscellaneous expenses like Home Owner's Association fees.
2. Shop around for a loan.  This can be difficult because you often have to compare apples to oranges. Watch for underwriting fees, fees to obtain your credit report, fees for the title company, fees for the bank or broker, title insurance, etc...  I believe that companies are required to give you a truth in lending statement that should outline all of these expenses.
3. Loan applications within 7 day period are consider 1 application for credit scoring purposes (something to keep in mind if you are going to shop around).
4. Once you have a good idea about how much loan you can afford, start going to open houses that are in your price range.  You don't need a realator to do this - but the realator that is hosting the open house is trying to hook in people just like you. Just tell them you are already working with a realator and they'll leave you alone (or just ignore them).
5. While looking, look for qualities in a home that you like, consider the obvious things like bedrooms, bathrooms, kitchen and yards. But don't forget the small stuff like age of the house, how much work you would have to do to make it liveable, is it clean, is the heating system older than you are (you can usually tell by looking), are the windows old?
6. Once you have a good idea of what you like, then contact a realator. They'll help you narrow your search down to your preferences and price range.
PM me if you have questions - I'd be happy to answer them.