It's nonsense having your AGP aperture set at twice your GPU's RAM. Set it at 128MB for all graphics cards of 32MB and above with more than 512Mb of main memory. You won't have to run your PC3200 RAM @ 2700 speeds as a matter of fact, your motherboard should be able to run your RAM at a percentage of your FSB, unless it expressly states this somewhere concerning your motherboard.
How much cache does your HDD have?
I really would recommend buying another 512 Mb of RAM however, XP can use a great deal of RAM if left for long enough just idleing.