>Peter,
>
>In the registry, I find interesting infos at:
>
>HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System
>
>Now, some users change their motherboard or upgrade their BIOS, but maybe not as often as formatting theire drive...

I hate to burst you bubble, but this subkey hive changes every time a new device is detected, or the Add New Hardware Wizard runs, or you reinstall or upgrade Windows, or you upgrade a device driver - at least as often as you reformat a drive.

Worse - it's likely that two identical machines built from a common standard build will have identical hives - ie, you go to Gateway and buy 6 identical workstations at the same time, they probably will all come from a common Windows system image.

With NT/Win2K, you could use the system SID, but that will most likely change each time you do a complete reinstall.