Don't buy if you can't stay put.
If you can't commit to remaining in one place for at least a few years, then owning is probably not for you, at least not yet. With the transaction costs of buying and selling a home, you may end up losing money if you sell any sooner - even in a rising market. When prices are falling, it's an even worse proposition. Make sure you discuss your plans with your Realtor so he or she can give you sound advice on this your biggest life-time purchase.