Outlook Express's message rules are stored entirely in the Registry. This tweak will transfer those rules to another machine, wiping out existing rules on the target machine.
On each machine, you will have to determine the correct subkey of the HKCU\Identities key. Select each in turn and check the Username value in the right-hand pane. Substitute the value there for identity in the key below.
Action: Select the key and choose Export from the Registry menu. With Win NT 4.0, use the REGEDIT4 format. Open the REG file in WordPad and use Search/Replace to replace the source identity string with that of the target. Delete the above key on the target machine using the target identity string. Move the resulting REG file to the target computer and launch it.