The specific kernel version sme server 2.4.18 has problems with the 845 chipset IDE controller. It reports a resource collision and won't allow DMA mode.
The solution I have found for Redhat 7.3 and Suse 8.0 is to update the kernel to 2.4.20 or later.
This is a widely documented flaw in the 2.4.18 kernel.
Is it possible to make a kernel upgrade available for SME Server 5.6, or some other way to get DMA mode working?
This issue has lost me hours so far- the install took about 9 hours due to being in PIO mode.