I recently got GA-K8N Pro motherboard and 2 Kingston's DDR 400 DIMMS of 512 MB each (KVR400X64C3A/512). Windows XP just wouldnt boot with this setup. I also replaced the Kingston DIMMS with Optima DDR 333 256 MB, and that works perfectly fine. I also used a different set of Kingston DIMMS in case the ones I got the first time were bad. But still, windows would boot