1. Turn off/on the router
2. Get into ROM Monitor  [Ctrl-break]
3. Change config-register to 0x2142 [o/r 0x2142]
4. Reboot [i]
5. Retrieve saved configuration back to working area
6. Change password to "class"
7. Change config-register to 0x2102
8. Save change

http://www.cisco.com/warp/public/474/