Forum .LRN Q&A: Re: Help Needed in Setting up .LRN to Scale
The biggest question is your disk IO. Just what is that "1 * 200 gb raid" exactly? If it is really a RAID 10 array with 4 or 8 disks or something like that, you might be fine. But I don't think that's what you have, and if my assumptions about your hardware are correct, it would probably only cost a few thousand dollars to buy a brand new and much faster Linux box.
Which isn't to say that your scaling problems are hardware related, they might not be. But when good server hardware is so cheap, it doesn't make sense to even try to run a large, high traffic site on a slow machine.