I'd like to mirror what AmigaDave and mdivancic have said and are experiencing. I too inherited a combination of IBM and Seagate drives from an old Dell server. Out of 4, I was only able to get ONE to ever work! And I've got the adapters w/ termination everyone else is talking about. I chalked it up to bad drives (I kept them all anyway), but am somewhat "relieved" to hear others have experienced the same things. I am currently using the working 16gb Seagate drive in my A2500 with zero problems however. When SCSI works, it works real well :-)
But I guess my next question is: why is SCSI so seemingly picky or flaky? Combination of things I guess - but frustrating when you know how to troubleshoot, but are left with no real answers.