hi jepeters,
I'm only familiar with the JetDirect300x external. On that one, unplugging it,then plugging it back in while holding the test button(for 5 seconds) will reset it to factory defaults. It will then show as an unconfigured device in JetAdmin. Here's a link for documentation etc for external ethernet Jet Direct Print Servers.
http://www.hp.com/cposupport/nonjsnav/jdexs.html
I'm know you can reset them from JetAdmin as well but I only use it at work so can't check it out until Tues.