DDR 333 is what they've got for RAM? That surprises me greatly. You might not need to add more than 1GB, but you would certainly want it to be the fastest RAM your motherboard can handle.
I can't speak to the striping performance issue from experience, but I can from reading up on it. Quoth Anandtech:
"If you haven't gotten the hint by now, we'll spell it
out for you: there is no place, and no need for a
RAID-0 array on a desktop computer. The real world
performance increases are negligible at best and the
reduction in reliability, thanks to a halving of the
mean time between failure, makes RAID-0 far from worth
it on the desktop."
http://www.anandtech.com/storage/sho...=2101&p=11