Sorted ("ish", but at least I can now print from the T61)
No, I didn't cheat by hooking up a USB or ethernet cable, I simply noticed that on rebooting the T61 the option for "use printer offline" is defaulting to "ticked". Untick it, and the printer's back on line until the next T61 reboot.
Hopefully I simply have a setting to change somewhere that I've missed so far though it's strange that this didn't happen with the original installation.
Stand easy.