Okay. Here some news for you. Since the edition of Windows 98 SE, Microsoft has implemented the ACPI-technology (=Advanced Configuration & Power Interface) into their operating system. The ACPI enables various sleep/standby options for the operating system. The following procedure might solve the problem for Win98SE / 2000 / XP
perhaps even without reinstalling windows.
Note: this procedure is NOT tested!

Following description only for Windows 98 SE, 2000 , XP!!!

To disable ACPI feature during installation:

·Windows 98 SE
start setup with the option:
setup /p i
Links to setup-switches:
http://support.microsoft.com/support/kb/articles/Q186/1/11.ASP

·With Win 2000 or XP:
Start setup. When setup asks you at the beginning of text-mode setup to press F6 to install SCSI/RAID-controllers press F5 and choose Standard-PC (=Non-ACPI-PC)

On a running system:

·Windows 98 SE, Win 2000 or XP:
change the value of the registry key: "HKLM\Software\Microsoft\Windows\CurrentVersion\Detect\ACPIOption" into "2"
To enter registry go to Run > Execute > type in "regedit". clicking on |+| HKEY_LOCAL_MACHINE (HKLM) will open that tree and so on ...
If this entry is not in your registry, go to "...\Detect" and create new DWORD-value "ACPIOption" by clicking
Edit->New->DWORD-value and typing in "ACPIOption" with value 2 (no matter if dec or hex)

After that - start hardware detect.
I guess this disables ACPI and enables APM instead.
Then disable APM.
Okay. I was not able to check this out since I don't have a Vaio Laptop. Someone with the same problems (random shutdown) sent me a link to a german page with general information about ACPI and APM.
What you can read above is my translation.
Perhaps someone can figure out, if this procedures do actually work.
Please let me know if you have some results! I'll publish them here.
mailto: strandi?web.de (change ? into @ - Antispam)

Here some links:
·ACPI/APM info page (german):
http://www.heise.de/ct/Redaktion/ciw/acpi.html

·Official ACPI-Page
http://www.acpi.info/index.html

Andi