@SlimJim
Okay, thanks all the same

I think the Linux/IDE thing is a known problem - I found people mentioning a problem that required them to disable DMA if the machine was to be vaguely stable.
I take it the UBoot firmware isn't finalized yet, either - it still seems a bit buggy... When you issue a reboot command from Linux, it tends to "forget" the environment variables unless you actually switch the machine off and on again. And then, apparently my onboard MAC address has changed of its own accord...
Since you mention it - dual boot is a bit awkward - you can have it boot into OS4 *or* Linux by default, but you have to halt it and issue a few commands (change the env variables etc.) at the prompt if you want to switch to the other OS.