Windows Updates should create a System Restore Point before installing the update, so you should be able to roll back to that.
How to restore Windows XP to a previous state describes the steps to rollback to a restore point and although is obviously Windows XP specific, the process should be similar for Server 2003.
Note that you can launch the System Restore GUI from a command prompt
but I’m not sure if it’s possible to execute an actual restore this way.
You could use wuinstall. It is a command line tool for managing Windows updates.
Although there is no explicit command for undoing the last update, you can uninstall updates in several ways. The basic command is:
wuinstall /uninstall ...
There are many ways to select the updates to be uninstalled. For example:
/match "regular expression",
The command for uninstalling an update with a known KB number would be:
wuinstall /uninstall /match KB1234567
For more info, see here.
wuinstall is not part of system commands, you can use
wusa /uninstall /kb:<number>
and to see man page try