Console to the router, power it off and back on, and within 20 second or so of powering it on, initiate a break (with Hyperterminal, ctrl-break or shift-break, other terminal emulators like PuTTy or Tera Term may be different). You will get the prompt
rommon1>
at which point you type
rommon1>confreg 2142
rommon2>reset
Let the router come all the way up, as it boots the default config. Answer no to the first question, and yes to the second (if it asks a second). Then...
router>en
router#copy start run
router#conf t
router(config)#config-register 2102
At this point, you can change the passwords, as even in the config they will be encrypted (if you used an "enable secret" password, or if you issue the command "service password-encryption). If you need help redoing the passwords, let me know. Also, don't forget to save the config, or you will be doing all this again...
router#wr
That's how you save it.
Burt