Ive had the same issue, unfortunately in my BIOS i cant disable speedstep, Vaio TX651p... I have noticed that on battery it runs teh lowest it can, and without a speedstep kernel it will start (and stay at 600) but with a speedstep kernel on batteries it hangs... plug it in, and its fine.
Can anyone think of what may cause the hang up with the speedstep kernel? its 8.9.1 - 8.8.1 semthex will boot fine!
That is now my only issue on the Vaio - I orded a Dell 1490 PCIe card for my wireless ($15!!), and will likely toss XP altogether if it works!