Desktop uprade wishlist

My PC may be only one and half years old, but I've already started feeling the urge to upgrade it. After starting most common applications, I find myself hitting that 384MB physical memory limit. And when I hear my hard disk clatter as I open files, I feel I could really improve my experience by buying myself a RAID-0 solution. So I peeked around a bit in my system and found out that it is an Intel 845 chipset based motherboard that can take a max of 512MB PC2100 DDR-RAM. The processor is a Pentium IV 2.5Ghz but I don't think I'm pushing the CPU anywhere close to its limit yet.

Using SiSoftware Sandra drive index, my 7200rpm ATA/100 hard drive clocked 44MB/s. I am investigating how much boost I could get with SATA RAID-0 and SCSI RAID-0. For SATA-RAID, I would just upgrade my motherboard and buy one with integrated RAID controller (VIA 8237 southbridge) for under $50. That will also allow me to upgrade memory easier. A couple of SATA drives with 7200 rpm would cost about $70. For building a SCSI-based solution, I would need a PCI-based SCSI RAID controller and a couple of disks. I have not found a good low-cost SCSI-RAID controller yet, but a pair of 10000rpm 18GB disks would cost about $50.