Well, just to report success, the SATA CD/DVD drive I bought in the hope that it would overcome my installation problems on my Abit AB9 Pro motherboard has done just that.
I can now successfully install any current relase of Linux (well at least the ones I have tried so far, Ubuntu, Suse, Mandriva and Slackware). It needs a reasonably up to date kernel to work but not the latest, latest, latest version.
You have to turn on AHCI in the BIOS (for some distributions, Suse seems to manage without this somehow) and, of course, connect the SATA CD drive to the main (Intel chipset) SATA interface which the hard drives use as well. You also can't then boot from "SATA CD" you have to boot from the actual CD drive detected by the BIOS, presumably a consequence of turning AHCI on.
From there on it's plain sailing, installations run with the nowadays
expected smoothness.
Strangely I found that the sata.i kernel (2.4.33) in Slackware didn't work but the 2.6.xx alternatives were fine. Other distributions I tried were all 2.6.xx kernels I think, you don't get a choice. I guess only the newer kernels have the Intel SATA chipset support.