Even though the rates may be risings you have to look at what that actually means.  Sure the jump from 3.75% to 4.25% might look like a lot, but ulitmatly for most people that's going to be around $50-$100 added on to their monthly payment.  In the grand scheme of things, that's really not so bad to get the house you want is it?  

Also, you have to keep in mind that rates could continue to rise and for the history of rates, 4.25% is still a great rate!  Try not to let yourself get caught up in a panic if your rates rise.  Talk to your lender about what the actual dollars and cents are per month.  That will allow you to make a better informed decision and see the real impact it's going to have.