Originally Posted by m2uk
The hotel is the Harbour Plaza Kowloon Hotel (19*21 Nathan Road).
I think you are either confused or got some wrong information. The hotel at 19-21 Nathan Road is the Kowloon Hotel. There is also a hotel called the Harbour Plaza hotel, but that is several km away in Hung Hom (not far from the old, semi-beloved Kai Tak airport). You would do extremely well to be sure which place you're staying at.
If it's the Kowloon, then Chungking Mansions is less than a block away. The laundry there, called Puritan Laundry, is fast an inexpensive (in by 9am, ready by 3pm), but don't expect shirts and pants to be pressed.
There is a laundry service with branches all over town and in many MTR stations (someone help me out with the name), and they will launder and press shirts, pants, and t-shirts for about 1/3 or 1/2 of hotel prices. 1-day service is available, but you'll pay extra.