If something as simple as setx CLASSPATH %CLASSPATH%;d:\jars\foo.jar doesn’t work, I won’t use it (All I want to do is globally set environment variables from the command line). I’ll probably cook up a quick Perl script for this, using Win32::Registry.

Update: My blushes. The reason setx seems to not work is because NT’s console will not reload the environment after a program changes it — opening a new console shows the changes just fine. Bad usability, but setx isn’t to blame — cmd.exe really needs a Unix-style export internal.