I am happy to report 100 percent success

Trustix was going ok, but I soon ran into the brick wall that is my Linux skills! I fell over at the installing webmin part, and just got frustrated. I then started looking at NAS distros and had a go with FreeNAS which looked like it would work, but when I transferred the hard disk into the NAS, it wouldn't boot.
The NAS is a Cyrix 200MHz with 16Mb RAM, VIA chipset and RTL8139 LAN adaptor, all built in a single headless board.
Eventually came across NASLite at
http://www.serverelements.com/ and encouraged by the reports it will run headless without a vid card, I gave it a shot. Installed it on a 250Mb disk hooked up to a desktop with similar chipset and NIC. Upgraded the NAS to 128Mb with an old PC100 stick I found in the garage. Once I transferred the hard disk into the NAS, it booted first time and is fully functional. Runs like a charm. The whole install is really tiny. The downside is no user management etc etc and security is nowhere. However, this device is well behind the firewall and will be used for backing up the SME server only. NASLite is a mix of open source and commercial so had to pay for it, but at 29 dollars (16 quid) it was well worth it to keep the NAS going a while longer.
I have lost the functionality offered by the LEDs ont he front of the NAS (disk remaining capacity, Ready, etc) but that's not something to lose sleep over I reckon.
Cheers,
Graham