I agree with what DMJulie posted, don't waste your time trying to dive north. Kauai catches big wave action in the winter and it usually shuts everything down.
On Kauai, your boat docks at Nawiliwili and it's about 15-30 mins. to Poipu from there - on a good day with no cruiseship in port (haha..) If you're planning to shoredive at Koloa Landing it's likely a drive from there to Aquatic(not sure where it is) or Seasports (been there) for tanks/gear rental.
Same advice on Maui with one exception. Most of the boats dock in Kahului which is a 45min drive from there to either South or West Maui where all the good shorediving spots are. If you're early enough to get on a boat, they all leave from Kihei (mostly Molokini) or the Lahaina (for Lanai) area. I don't think you'll be in time though as some leave as early as 6am to beat the tradewinds coming back around noon. A lot of them do afternoon dives closer to Maui so that's another option there. If you're traveling with non-divers, they could shop in Lahaina or Kaanapali while you're gone - the cruiseline likely has buses to there also.
If not, there are some good shore dives south of Kihei in the Wailea area or scattered along the coast from there up to about Kapalua. In the Kihei area, try to hook-up with Shaka Doug, he runs a divebus for shorediving. He's on Scubaboard also. It's about 45mins. drive up the coast from Kihei to Lahaina also, more if whales are spotted along the road - that can slow things way down. (I think they're already in the area now)
The one exception is that I've read that there's at least one cruiseline that makes port in Lahaina now. From there you could walk to Lahaina Divers or Pacific Dive. Mala Wharf is also walking distance from there - maybe not with a tank - I don't remember exactly.
I've never dove Oahu, but assuming that you dock in Honolulu, I know there used to be diveops that picked divers up in Waikiki, maybe they do at the port also. Might be worth checking.
Check out
www.shorediving.com for sites on all the islands.