Somehow, unbelievably, my problem is solved. After about 18 months of this garbage msm boot-rom post issue, it is gone. I am going to describe what I did, but somebody is going to have to tell me why the issue disappeared.
Some more details: Asus P5B-E, rev 1.02g, BIOS 1202 (I think), 2 Seagate ST3320620AS 320GB 7200.10 16MB cache SATAII HDDs in RAID 1 in SATA ports 0 and 1, 2 SATA Lite-on DVD burners in SATA ports 4 and 5, Vista Home Premium (32 bit).
The issue - 1-2 min bootROM POST time, one drive now showing as failed in intel's matrix storage manager (MSM). DVD burners disconnected from SATA ports during all troubelshooting.
Installed newest msm windows driver 8.6 in Vista. 1 drive showed as failed.
Pulled the drive marked as bad so only 1 HDD in RAID 1: msm boot-rom showed array as degraded, but bootable, still had long bootrom post time, Vista boots/runs fine.
Pulled good drive and reinstalled bad drive: still long POST, no O/S boot.
Pulled working Western Digital HDDs from a system running Vista 64 in RAID 1 on ICH9R southbridge and installed in this system: instant recognition; 1-2 secong boot-rom post time, Vista even booted to the logon screen (that's as far as I went with that setup).
Pulled WD array and reinstalled 1 working Seagate HDD: long POST.
Installed bad Seagate HDD in separate system and ran Seagate SeaTools for DOS diagnostics: both short and long tests PASSED! WTF - the drive is fine?
Reconnected "bad" HDD by itself on P5B-E: instant recognition! but no boot.
Reconnected good HDD with "bad" one: instant recognition in Boot-rom, shows RAID 1 as degraded, but bootable. Vista boots. Logon is OK and intel driver shows that RAID rebuild is in progress! After about 2 hours, rebuild is complete.
Ugh. I guess I'll know for sure if there is a compatibility issue with these HDDs in a week or two, eh?
Shutdown, reconnect DVD-burners, restart: instant boot-rom recognition, array is good, system boots normal!
Can anybody explain why the system now boots/works the way it is supposed to? Specifically how the heck testing a drive marked as bad and reinstalling it in a broken array fixes a boot-rom glitch? I would really like to know! Because I had this delay issue from the time I first assembled this system and both drives were OK in the array!
Ugh. At least it works. For the time being, anyway.