You should be able to lock into a rate for a short period on a pre-approval. We're house-hunting too. I have three weeks to use my relocation benefit from my new employer. Buying a house sucks.
Don't know whether they'll go lower, but they're now at the lowest rates in more than thirty years. My advice is, don't get greedy; do it now. And if you can, go for a 15-year loan, not a 30-year one.
Finance friends of mine think that within a couple of years interest rates will be 8% because of the budget deficits/debt that will cause the federal government to borrow more.