Remember, sometimes, it's not the Quantity of RAM but the QUALITY of RAM. Yes, a minimum is required, today at least 1GB. 2, and you're sitting pretty. The speed of RAM does make a big impact on overall system performance You don't have to buy the top-end muskin redline RAM to have a great gaming experience, I'm proof positive of that. I bought Level 1 ram back when they had a much more convoluted naming scheme for thier ram. Now they have three simple categories, the Green general purpose RAM, the blue high performance RAM, and the Redline extreme performance RAM. Most people can get away with the green performance, but the timings on the chips could be much better, which the blue ones provide in spades. I'm just using them as an example, and I've used Kingston, Crucial, Viking and Mushkin brands and I like them all pretty well for thier specific uses.
As for RAID-0 I thought all of the drives had to be the same size, otherwise you'd be losing 40 GB to wasted, dead space because the array must be created amongst the same size of drives. And no, you cannot partition a hard drive to get that 40 GB of space, because the RAID controller basically takes over those drives entirely. I could be wrong about this, but I'm pretty sure this would be a waste of time. I tried slinging my two 60GB drives together in a RAID array and it just wasn't worth the risk to lose all the data on those two drives. I left them in standard IDE mode and they function just fine. I never really saw a speed benefit with those two in RAID 0 myself, so I don't know if you would either. Also keep in mind that you would have to format all of those drives to get them into the array, because the controller will "format" the drives to be put into the array. You'd have to lose everything just to get set up, and IMO, for home use, it's not worth the hassle. I just partition the hell out of my drives.