After installation, the same problem occurred - no video. So I plugged my PC into a venerable 17" CRT monitor and I was able to see things on the screen. Unfortunately, after changing the video settings, the damn thing did exactly the same thing again when I plugged it back into the LCD. So I found myself an NVidia GX5500 or something similar - nothing special but does the job. So I can see Windows 7 in all it's glory, except that it doesn't recognise the onboard NIC so I replaced that too. Yay! Now I have networking. Time to use this baby for some actual stuff - better install Office 2007.
Part way through the installation - BSOD. Gone. Unrecoverable error. Reboot - same thing. After several tries I gave up and re-installed the system. We'll see how it goes this time :-)
On the plus side, Windows 7 is much quicker than Vista could ever hope to be. I mean, it's actually usable on a Celeron 2400! Resident memory usage is quite low, under 500MB which leaves plenty for actual software to run! Exciting I know. Further updates to follow once I get it re-installed.