How can I permanently append an entry into the system's PATH variable, via command line?

What I need to do:

• Append a folder to the %PATH% environment variable at the SYSTEM level.
• Make the change permanent.

How I need to do it:

• Using the command prompt, or another method by which all necessary commands can be written to a .BAT file.
• Using only tools which would be available on a bare install of Windows XP SP3, without Internet connectivity.
• I'd rather run the script locally, but I do also have remote access to the target systems. Bear in mind though, that I cannot presume any non-default services (i.e.: Remote Registry) are enabled on the systems.

Systems the script needs to work on:

• Windows XP SP3
• Windows Server 2003 SP2
• Windows 7 SP1
• Windows Server 2008 R2 SP1

I'm fairly familiar with the SET command, but I'm also aware that it will generally overwrite the existing variable instead of append to it. That is not acceptable. Is there another tool (or option for SET, which I'm unaware of) that will append to the variable instead? Or, do I need to put a work-around in the script that includes temporarily copying the existing variable to another variable or text file?

Also, it's my understanding that SET will not permanently alter the variable. I've seen mention of SETX, but that does not seem to come built-in to Windows XP SP3 (or, at least, it doesn't appear to be available on the system I'm working on). Is there another way to make the change permanent, via registry edit or something?

I've done some looking around and have learned a good bit from here about setting environment variables in Windows. However, I haven't yet found an exact duplicate question that will suit my needs. If there is one, please do let me know.

The following adds 'C:\bin' to your path and then saves the new path into the Registry:

set path=%path%;C:\bin
reg.exe ADD "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" /v Path /t REG_EXPAND_SZ /d "%path%" /f

Note that the quotes around %path% are optional assuming the path does not contain spaces.

I only tested this on XP SP3, but it should work on newer version as well.

I guess a new user who logs on before the machine reboots may not get the new path.

Harry is right with his comment about %SystemRoot%, if you want to keep these, you need to pull the old value for path from the registry first:

@echo OFF

set KEY_NAME="HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment"
set VALUE_NAME=Path

FOR /F "usebackq skip=4 tokens=1-3" %%A IN (`REG QUERY %KEY_NAME% /v %VALUE_NAME% 2^>nul`) DO (
  set ValueName=%%A
  set ValueValue=%%C
)

if defined ValueName (

  set newPath=%ValueValue%;C:\bin

  reg.exe ADD "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" /v Path /t REG_EXPAND_SZ /d "%newPath%" /f

  set path=%path%;C:\bin

) else (
    @echo %KEY_NAME%\%VALUE_NAME% not found.
)