After a little hassle, I now have it working nicely

It wouldn't update the ROM from the Strongbolt CD, so that idea had to be abandoned after multiple attempts.
I then setup a DSL vmware image and followed your instructions for upgrading the ROM over a serial connection. That didn't work either! It uploaded the rom image but when I issued a "write_eeprom 0" it just sat there. I left it for quite a while and then took the plunge and turned it off and on.
It booted back into 2.3.39 and was still working! I went back to basics and tried logging in as root over the console, hoping to try various password combos until one worked. No password was needed! If only I had known it was that simple all along. Doh!
Ftp'd over the flashtool and rom image and hey presto it is now all working perfectly.
I now have a beautiful yellow firewall ready to replace the "other" blue one

For reference, the ethernet ports get assigned as below:
Inside - eth0 - GREEN
Outside - eth1 - BLUE
Aux1 - eth2 - YELLOW
Aux2 - eth3 - RED
A little peeved that the port labelled "Outside" didn't end up as the RED though. Can that be easily changed?