The command that should normally allow you to change the serial number of Windows is:

     sysprep -nosidgen

The sysprep utility is part of the Resource Kit.

It is not certain whether there are some versions (OEM or other) where this would fail and even going back to the old number might fail, so do have a complete backup before you try.

Windows XP Recovery Console

The Recovery Console, sometimes casually referred to as repair console, is a tool that can help you to bring your Windows installation back to working order and to manipulate or copy files that cannot be copied while Windows XP runs.

It can be installed from the Windows XP installation CD, but is then not automatically updated by later patches or service packs. So the simpler method is to start it directly by booting from the installation CD and choose the Repair Console.

The Windows registry is a special database that keeps settings for Windows and other programs.

You can make changes to the registry by using a registry editor like regedit.exe, the older regedt32.exe, or a third party registry editor.

A minus sign inserted directly after the opening bracket in an otherwise normal .reg file removes that key. It works only for keys, not for values, but you can remove, then recreate a key. Example:

[-HKEY_LOCAL_MACHINE\Software\Adobe]

This entry in a .reg file will remove that entire key and all of its subkeys and values.

You can remove a value by entering a minus sign (without quotes) as the new value. Example:

[HKEY_LOCAL_MACHINE\Software\TestKey]
"TestValue"=-

This removes the value named "TestValue", but leaves the key "TestKey" in place.

REGEDIT.EXE imports and exports registry files to and from the registry. Usage:

REGEDIT [/L:system] [/R:user] filename1
REGEDIT [/L:system] [/R:user] /C filename2
REGEDIT [/L:system] [/R:user] /E filename3 [regpath1]
REGEDIT [/L:system] [/R:user] /D regpath2

/L:system – Specifies the location of the SYSTEM.DAT file.

/R:user – Specifies the location of the USER.DAT file.

filename1 – Specifies the file(s) to import into the registry.

/C filename2 – Specifies the file to create the registry from.

How can I move my installation to a bigger hard disk?

Partition Magic by PowerQuest is indeed a wonderful solution for your problem.

More than 2 GB Address Space

The following text is courtesy of Bruce Sanderson, MVP.

Windows Explorer command line switches are documented in several Microsoft Knowlege Base articles. The best one is probably this:

HOW TO: Customize the Windows Explorer Views in Windows XP (Q307856)
http://support.microsoft.com/kb/307856/

The simple way

You can change the local drive letters in Start, Control Panel, Administrative Tools, Computer Management, Storage, Disk Management.

Changing the drive letter of a boot or system partition

Changing the drive letter of the drive that contains the boot files or the operating system is more involved.

Check the following article in the Microsoft Knowledge Base:

An error message informs you that you cannot move or rename the Documents and Settings folder
http://support.microsoft.com/kb/314843/