"google" the following text for a good article on the 3.4L engine failures. Should come up as first in list.
...exploding myths 996 engine failures...
or check the following pdf link
www.autofarm.co.uk/pdf/Total911_July06.pdf
Written by a Philip Raby (any relation?) Cites work done by Autofarm and JZ MachTech, two specialists in England.
Good info and explanations on the issues. Even identifies the slow coolant leak.
Found it when researching my new baby, a 2000 996 brought home this weekend! WOOT!