Thank you for your question.
If you don't have a real estate agent assisting you, that is absolutely the best bet for you at this point - find an expert to explain how the whole process goes and to assist you throughout the home search.
Generally speaking, you may request a showing at any time.
In this market, because of the complexities of financing, I would strongly urge you to contact a few lenders before you start looking in order to nail down your price range.
Further, any agent who IS listing and/or showing a property is going to ask you whether you are pre-approved yet - it's an important question.
It works out way better for everyone if your answer can be "Yes!"
Matt Laricy is right. You will get deluged with phone calls, but remember that no matter which agent you choose, they're going to want to be sure that you're pre-approved, and I can certainly help you with that.
Please feel free to give me a call or go to my webpage to fill out an application. (www.mattbukovy.com)