Ok, yes the thermostst housing bolts to the Water Pump.
Yes it can be complicated job, the complication is making sure the timimg marks are in the correct position.
You will have to remove pretty much everything from the front of the engine along with the Radiator(for room to work).
If you are considering attaching this job, I will suggest you keep a digital camera handy and take plenty of pic. Place bolts and nut in baggies and mark what they are for.
Also since the Timing Belt was changed about 15k miles ago, you should be ok to just replace the water pump. I won't usually do this type of job unless I change everything, water pump and timing components, when the water pump is run by the timing belt.
Below is a diagram for aligning timing marks.
Image (Click to make bigger)
Saturday, January 8th, 2011 AT 11:53 PM