Aloha from Maui... I also recommend the Maui Revealed book. You can get it in pretty much any major bookstore these days.

If you plan on taking a day trip to Hana, here is what I recommend:

1) Leave Ka'anapali at 7am (as in be in your car on the road at 7am). It will take 45 minutes to get to the start of the road to Hana. Make sure you are wearing a swim suit and layers of clothes that can be used for hiking. Bring hiking shoes, towels, bottled water, bug spray, sunscreen, some snacks, maybe a backpack, and definitely bring a change of clothes.
2) On the road to Hana, only stop to take pictures of the big water falls and the occasional pull-offs for pictures. Enjoy the drive but don't waste too much time.
3) Following the instructions in Maui Revealed, take the short excursion to the Keanae peninsula. There is a snack stand that sells the best homemade banana bread on the island here. Continue past the snack stand to the end of the peninsula by the baseball park and the old church. Stop for a few minutes to stretch your legs, eat your banana bread, and take in the ocean view.
4) Continue on the road to Hana until just before town, you will see a sign for Wainapanapa State Park. Turn left and drive about a mile until you arrive at a parking lot. Turn left and continue driving to the farthest end of the lot. Park here and you will be very close to two points of interest.
5) First, immediately to the left of where you parked is a large wooden sign with a story on it. Read the sign and proceed on the loop path (either left or right). You will come to an underground lava tube that is filled with clear fresh water. I highly recommend you take the plunge into the water from the ledge. The water is about 5 feet deep so be careful. Swim back to the back of the lava tube.
6) Second, after you have fun in the lava tube, go back to the wooden sign and continue walking until you get to the black sand beach. Warm up on the sand here. You can play in the ocean but the current can be strong so don't go very far out in the ocean here.
7) Continue on to Hana and drive through town. If you are starving and it's close to lunch, stop in Hana for lunch either at the general store or one of the few restaurants (see the Maui Revealed for options). After leaving Hana, continue about 10 more miles until you reach Kipahulu State Park. It will cost $15 to enter the park and park your vehicle. There are restroom facilities here but no potable water so make sure to bring your own refreshments. Here you can go to the so-called "7 sacred pools" but there are more than 7 and there's nothing sacred about them. Personally, I would skip this in favor of the hike to some of the most beautiful water falls you will ever see. The hike is 4 miles round trip and takes 2-3 hours. Do not start this hike after 3pm.
8) The trail head for the hike at Kipahulu is on the other side of the road from the parking lot. The ranger station can point you in the right direction to get started. There are plenty of signs and the path is very obvious. Follow the trail up the mountain until you come to the Makahiku Falls about half a mile into the hike. The Makahiku Falls are 200 feet tall and you can see them fully from the first overlook you come too. If you are more adventurous, there is a sign saying "stay on the trail" with a bunch of warnings just past the overlook. If you follow this "forbidden" path, you can walk to the lip of the waterfall itself (if the water flow permits). Be very careful of flash flooding as there can be a sudden shower on top of the mountain and you'll never know it until the water level suddenly rises. If you are even more adventurous, it's possible to swim up the river through three pools (only attempt this if the water level permits). At the end of the 3rd pool, you will come to a small waterfall and an extraordinarily deep hole in the ground. DO NOT ENTER THIS POOL UNLESS THE WATER LEVEL IS AT OR VERY CLOSE TO THE LIP OF THE ROCKS YOU ARRIVE ON. If the water level is at or no more than a few inches low, you can cliff dive in this pool as it is at least 20-30 feet deep. There are no hidden rocks that I am aware of. The best place to cliff dive is on the other side of the pool and you must climb the rocks to the left and circle around under the waterfall to get to this point. Again, this area can be very unsafe for inexperienced hikers and swimmers. I am not advising you to do this but it can be quite an experience if you choose to take the risks.
9) Continuing the hike on the main trail, you will come to a very large Banyan tree. This is one of the largest of it's kind in the world.
10) Past this tree, you will eventually enter into the bamboo forest. This is a very beautiful and serene area. There is a boardwalk in this part so you don't have to worry about mud.
11) Once you have left the bamboo forest, you will eventually come to the end of the trail which is at the base of the 400 foot tall Waimoku Falls. These are the highest falls in Maui. There is a very shallow pool at the base of the falls. It's a great photo op to stand in the falls but be very careful of falling rocks. I've had several close calls here. This is a great place to stop and eat some snacks and rest a bit before heading back to the car. Make sure you are heading back to the car by 4pm at the latest. Depending upon how much time you took at previous stops, you could be back at the 7 sacred pools in time to swim before the park closes.
12) On the way down, there is a guava tree forest on the right side of the trail. You can cross over to that area pretty easily and eat fresh guava's if they are ripe. Ripe guavas will fall off the limb of the tree with a slight pull or whack with a stick. Some are very very sweet while others are tart. If you get a tart one, toss it and find another.
13) Once you are back at the parking lot, change clothes and get comfortable for the ride back to civilization. Make sure that whoever is driving can handle the drive back and you may have to switch drivers periodically. If all goes well, you should be back in Kahului by 7 PM and back in Ka'anapali by around 8pm.

[This message has been edited by aero96 (edited 5/11/2009 2:39p).]