We have a new client and have taken over a leased line with 2 x 1603 ISDN routers.
We don't know the passwords and would like to recover/replace those without losing any settings. I have found these instructions: http://www.cisco.com/en/US/products/hw/routers/ps214/products_password_recovery09186a0080093e11.shtml#NetPro but am not clear on whether any config will be lost.
Is it possible to save the config to an external device to make sure ?
Also are there any other passwords I should be aware of ?
You won't be telnetting onto the router rather you should be doing this with a console cable connected from a com port on your laptop to the console port on the router.
The password receovery procedure in your doc assumes you have no passwords so it shows you how to bypass all passwords - thats what the bit about hitting the break key and going to ROMMON is all about.
When you do get in and reset the enable password you should also reset the line password (which is used for remote telnet access) eg.
router(config)# line vty 0 4
router(config-line)# password 0