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According to Disney Hollywood Hotel's webpage, it is within walking distance from the Disneyland. But after doing a bit of research, unless there are shuttle buses from the hotel itself, it seems that there is no inexpensive solution.

You could take the E32 airport bus and then change to the bus number R8 at the Lantau Link Toll Plaza. This way it will cost just HK$10+$6 = HK$16 per adult and HK$5+3 = HK$8 for the child. Hence by bus it is a total of HK$40 (about US$5.50) for 2 adults and a child. It is quite troublesome when you have lugguage. There are usually very few people at the Lantau Link Toll Plaza bus stops. (For more info: follow the Disney link on this page.)

According to information found at the hotel's website, taking a blue taxi from the airport will cost about HK$100 (plus charges for luggage). It may be a good idea. After all you are on vacation! (See this page.)

To get to the MetroPark Hotel Mongkok, for HK$32 per adult, bus R21 is probably the cheapest solution. According to the CityBus webpage, there is a stop in front of the hotel (See this Disney page & this CityBus page.)

Yes, of course you can visit Ocean Park for half a day, but according to the Ocean Park website, there is just one price for admission - no half-day passes. (See Ocean Park website for more details.)

To get PSP and iPod with a waranty, I would suggest you to go to a chain store (see this page) because it is not worth getting a bargain when you may get a lemon. But if you like the risk factor, the Golden Computer Arcade in Sham Shui Po is where you want to check out.