When we were getting ready to book our first Alaskan cruise it was a similar situation. We could go Sat. to Sat. or Sun. to Sun. on a specific week (also in August). Since you seem to be locked into Aug. 24th, which is a Sunday (Saturday departure no good?) you'll find it will limit your choices greatly.
One thing you need to research and decide is are there any "must do" items. In our case Glacier Bay was a must. This again greatly narrowed our opportunities.
I would suggest as a start to go to Yahoo Travel or Expedia or any of the travel websites and plug in that you want a cruise in August, 2003 to Alaska and it must be a 7 day cruise. You will then see all the August options. Then you can narrow further by sorting out the August dates that don't fit. Then you can sort more if you have any requirements such as I did with Glacier bay. This should really narrow down your decision. Once you've decided you can even price it out to get a general idea although I think booking thru a Cruise Specialist Travel Agent will probably do better pricewise and cabin location.
I've found reading these sites that there are so many different opinions on Lines, services, individual ships, that it really is an individual preference and that since you've never been on a cruise you should take all of our recommendations with a grain of salt. For example, if you think it's important to have the same wait staff every night at dinner you may not want NCL's Freestyle. Or if you don't gamble, someone loving or hating a ship because of the casino is irrevelant to you. Some people (like me) think a balcony for Alaska is a must and others think that inside cabins are great and they can do all the scenery viewing up top. Again, it's all personal preference. What do you think you'll like is important to start with. You mention that you want the ship to be like a "5 star resort". I've sailed on RCCL, NCL, and HAL and thought that they were very close in quality/service/food (HAL's decor a bit classier). I'd get a lot of arguments about that statement. Again, it's personal preferences.
You will have to discover for yourself your personal cruising likes and dislikes and for your next cruise (and there will be a next cruise I'm sure) you'll be able to narrow don't your search even more.
In our case, we had narrowed it down to 3 choices and opted for the choice with the best price AND the best cabin location (which was luckily the same ship). And no regrets at all.