Depends on your preference, you can take the airport express train to the Kowloon stop and take a short taxi ride to the hotel. If not much lauguage, you can take a express airport bus #A21, almost door to door, and since it travel through Nathan road, you can have an idea where to go too.
Since the time is short, best bet is the 3 street in Mongkok, you can take taxi or 3 stop for subway
http://maps.google.com/maps?f=q&hl=e...wloc=addr&om=1
All 3 are parallel to Nathan Rd, 1st is Sai Yeung Choi St, all the latest electronics, 2nd is Tung Choi St, the famous ladies market, but not just stuff for ladies, 3rd is Fa Yuen St. consist of good places to eat and sneaker shops.
If you're geeky enough, you can spend half a day in Mongkok Computer Centre http://en.wikipedia.org/wiki/Mong_Kok_Computer_Centre which is between the 2nd and 3rd st.
You can spend the other day just walking around TST with it's many high class stores and malls.

Good luck!