UPDATE: I think that information below are not correct because in days after this post, I continued to have this problem in other scenarios too. At the end of the story I just re-installed the machine with a "Vista&SP1 integrated" and now, after one month, everything is working fine. At this time the only hypothesis I have is that for some reason the SP1 setup didn't the right job, how knows:-S
Since I installed SP1 RTM on my Vista (Toshiba Tecra M7 dual core tablet PC) I discovered that the system after a boot, remained with CPU usage constant at 100%. A deeper analysis shown that 99% of that CPU usage was kernel time:-(
After a Sunday afternoon spent to find a solution, I discovered the problem: I have an old PCMCIA card reader from GEMPLUS (GemPC400) that, if present when I boot the laptop, produces the issue and the behavior described above.
When Vista started with CPU ad 100%, even if I removed the card reader, system remained with CPU at 100% (== unusable). The only way to unlock the situation, was to reboot the system (without the card!).
Because I needed that card reader, I found a workaround: infact, if I start Vista without the card reader and after the boot I insert it into PCMCIA port everything goes fine.
Lession lerned: if you discover that your Vista uses 99% of CPU time as "kernel time", try to analyze peripherals you have installed because there could be a driver that is not working as it should.