I agree with the others. First of all, adopt an adult dog. There are many many wonderful even younger adult dogs who were abandoned simply because of the economy who are great with cats. If you know what breed you want, do a search that breed rescue in your area - they will tell you whether or not a dog you are considering will deal well with your cats. If you just want a furry companion - your local human society or www.petfinder.com is a great resource.

As for the dog being alone most of the day - as long as you don't mind coming home every night to walk him (or hire a pet walking service to do it), he'll be fine. I think it's much more important to have a very loving home than it is that you're home all day - if that makes sense.