1. Desktop P4. Willamette (socket 423), Northwood (socket 478) and Prescott (socket 478 and 755) cores.
2. They sit in notebooks. They make the keyboard really hot. IIRC, they are the desktop ones, with either lower voltage or constant clock speed changing to keep from using tons of power.
3. Highly efficient mobile chip. A 1.4GHz one is around euqal to a desktop P4 2.2GHz. Up to 2 GHz now. They use under 30 watts under full bore (Prescott 3.6GHz can use near 150w, if some sources are correct). When combined with an integrated 802.11b, it's Centrino. New Centrino likely to use 11g, and probably 11i later on. Expensive, but if you really use a laptop on the go, the only other game in town is Transmeta, and they don't exactly have stellar performance.
4. Yup, #2.