If you are interested in Niah National Park, or trekking in Sarawak generally, you should visit the Trekking Sarawak websitehttp://www.sarawaktourism.com/TrekkingSarawak.
TrekkingSarawak has heaps of information about all the main national parks in Sarawak, including practicalities (accommodation, getting there), detailed trail descriptions, info on plants and animals, myths and legends, lots of photos, etc, etc).
The Mulu pages are still being developed, but there is some general information and photo galleries from Mulu already up and running.
My spouse and I made the website last year, and are still updating it. Hope you like it! I would welcome any feedback on the website (see the "feedback" or "contact us" links on the website).