you want cpu clock speed multiplier at 12, and FSB at 2.
More to the point i have a KT600 chipset on my mobo, and a 2700+xp athlon. Im sure your cpu is having no problems, but that mobo chipset surely can't take up to 400mhz FSB mine can only take (well its on 2x 169 atm).
I realise this would be a costly suggestion, but new mobo and matched ram with relevant FSB speed.
On another note those errors with the ide / hdd? Im not quite sure how they fit into all this. And you say they are the common ones that come over and over? If you can (and you know how to use it) get yourself a knoppix disk ( http://www.knoppix.net
) and scan the disk for errors. But I'm certainly not in the know about hard disk errors, over to the rest of you.
Summary, get rid of the 266mhz ram because it will be screwing your pc anyway (although being as you're on a KT400 chipset maybe lower your other stick to 266 aswell and see if it's any better) But as everyone else says, you want your ram speed and FSB speed the same, and as high as you can.