you can buy 2x2GB (4GB total) DDR2 800 RAM for $20 shipped on ebay. Getting faster memory won't be a problem if it is cheaper than the DDR2 667 stuff. Just make sure it is DDR2 (and not the smaller notebook SODIMMS)
For the HDD you are probably best taking the effort to reinstall windows and all your apps with the new drive- a good cleanup can make for a faster pc in itself
