Firmware upgrade tools
Tools that run under Windows:
This is a menu-driven Windows tool. It detects multiple network adapters and offers a choice. Select the one the slug is attached to. When it detects the slug it will probably display it's original name (as printed on the base) and not the name you may have set in the configuration screen.
As far as I'm aware the Sercomm upgrade tool will never overwrite the bootloader so if an upgrade fails you simply put the slug back into upgrade mode and try again.
As of January 2007 the tool appears to have been removed from the Sercomm website. Hopefully someone will build one of the Linux tools to run under Windows.
Tools that run under Linux:
The first Linux based upgrade tool. I have not tried this.
The second Linux based upgrade tool. Like the Sercomm tool this one will not overwrite the bootloader unless compiled with special options set. Upslug2 does not use code from Upslug. You are most likely to receive this as a source "tarball" file. It's not hard to compile it under a typical PC Linux, and you can run the resulting binary file in place, it does not need installing. It does need to be run as ROOT though, so I use sudo to run it.
If you have two slugs you can even run Upslug2 on one slug and use it to flash the other.