Assuming the eth?/? interface has already been configured and given an IP address...

1. Start a local TFTP server
2. on router (telnet or hyperterm) en (enable) pass
3. copy tftp flash (RETURN)
4. prompted for IP of TFTP server

Follow prompts...

IMPORTANT:
When loaded, DO A WRITE TWICE
The first write will warn about overwriting a confi written by a previous IOS.
The Second write will clear and flush the config with no warnings.

Caveats: Need to have IOS .bin file in the TFTP local upload directory. Also need to know the .bin name - easiest to copy and paste this as they're long and unwieldly.