A couple of points for clarification:
- "Centrino" is
not a CPU. It's a marketing brand for the combination of Intel's wifi technology & CPUs.
- miniITX is only a form factor. It has no bearing on CPU or anything else. You can get a miniITX motherboard with a low-power Via C3 or a uber-fast Pentium M and soon an Athlon64 AM2.
Now, on to the answers!
A) Yes, the performance will be
far superior to an M10000 (the 1ghz C3 CPU).
B) Definitely!
C) Sure.
D) Laptop intalls have more issues than a desktop-style PC installation.
Really, I suggest perusing the forums as you plan. Search for laptop installations and ask some questions to the installers/owners to get an idea of how they overcame laptop hurdles.