You can use the MS utility "Setx" to make permanent changes form the command-line.
Here's a direct link to the Windows 2000 version (works in XP, etc.).
You can also get it in the Windows XP SP2 Support Tools pack.
not part of the standard Windows XP
setup but a command-line tool called
setx.exe is included in the Windows XP
Service Pack 2 Support Tools. This
tool extends the set command so that
permanent changes in the environment
variables can be made. For example, to
add a folder C:\New Folder to the
path, the command would be setx path