Help with upgrade suggestions

[merrlis]

Hello all,

I am looking to upgrade my CPU and or my motherboard preferably just my CPU and am looking for suggestions. Here is what I have.

Intel P4a, 2400 CPU (CPU Alias Northwood, A80532)
Intel Grantsdale i915 motherboard chip set (Maker Albatron)
2g Ram 133MHz Current clock 2400 using 4 512kb sticks (Max clock 3066) 4 slots Upgradeable to 4 but running XP so not sure if i will get full benefit
BIOS Award (5/12/05) Phoenix Tech (512KB)
Video: Nvidia Geforce 6800 GT (256MB) PCI-x

Looking to stay under $400

Thanks In advance