I am going to have to agree with Scott. In this market, you absolutely want to sell your home first! Unfortunately since most homeowners enter this process in the reverse, it is difficult to understand. In an appreciating market, sellers are much more likely to accept a contingent offer because there is a high probability your home will sell quickly. However, in the market we are now in, very few sellers will accept this type of offer. There are a few reasons for this. First, the obvious reason is because the chance of your home selling quickly are not as probable. Also, if the seller accepts your offer for a specific period of time while you try to sell your home, it hurts him (the seller). Their home is still on the market, but is listed as "under contract." Very few agents or buyers will then pursue a home that is listed this way. So in theory, it is essentially no longer on the market.
I would definitely say you should get your home evaluated, then listed asap. If you make the sale of your home contingent on finding a new home, then you don't have nearly as much pressure. Chances are, if you list your home at an aggressive price from the start, it will sell quickly and you can then pursue the new home. If for some reason during this process, the home you are keeping your eye on is sold, you then have the option of removing your home from the market or pursuing another.
I hope this helps a little. If I can assist at all or answer any questions, feel free to call/email me.