though scsi is necessary, could you try knoppix without scsi? the beauty of knoppix is that it will run from a cd, so drives aren't needed. if you did this, you could atleast find out if the raid controller is what is messing you up, or if it is the motherboard itself, etc.
if this doesn't work, i would strongly reccomend using the regular knoppix distribution as opposed to knoppix STD. there's nothing wrong with STD, but plain knoppix usually has better support -- though it is rather rare, sometimes the knoppix distro will have support for something that knoppix std will not.
you also mentioned that mandrake got a black screen of death... when did this happen? did you have the gui open; did it even open? orr.. can you not even get a console to type in?
as a final suggestion, even if you do not get gentoo, the gentoo live cd has some of the best hardware support there is. if you could download the latest gentoo live cd, maybe that will work, go from there and you may be able to find the problem. here's the folder for the livecd:
would suggest getting universial as it has more utils that come with it for operating, but if download size matters minimal is small enough.
good luck, LMK