[CentOS] Problems with IDE RAID on specific motherboard

About 9 months ago, I made a policy decision to adopt RAID 1 on all systems I 
admin. (about 20 systems, all told) It's been a long, slow process. 

One of the systems is being upgraded from CentOS3 to CentOS4. It's been 
rock-solid stable for over a year. It's a "frankenserver" with parts from all 
over the place, maintained over years of active service. 

Currently, it's got an ASRock "M810LMR" motherboard in it. 
http://www.ciao.co.uk/ASRock_M810LMR__5410842

When I install the O/S (I've tried CentOS 4.0 and 4.2) with IDE RAID, it 
bombs, takes hours just to format the drives, and won't reboot, getting stuck 
at "GRUB". But, when I install the SAME TWO DRIVES without RAID, (eg: some 
partitions on one drive, some on the other) it works perfectly. 

I've tried putting both drives on separate IDE cablels, using completely 
different drives, and trying CentOS 4.0 and 4.2. 

When I try to set up IDE raid while it's taking a very long time to format the 
drives, I see lots of errors about DMA on the alternate consoles, and there 
being only one drive (unable to start RAID array, only 1 drive found) even 
though the installer and disk druid have no problem reporting both drives. It 
comes down to something like "/dev/mdN delayed until /dev/mdX is synchronized 
because they share physical resources"... 

I'm stumped, and falling back to non-RAID because this system is needed in 
production. And, I'm not new to using software RAID, I've been using it for 
years without issue. 

Any idea what's going on? 
-- 
"The best way to predict the future is to invent it."
- XEROX PARC slogan, circa 1978