Reading problem is a tricky thing. A friend of mine had problem like yours. He posted his question on a computer forum. Ht was told that the loaction where you have your memory installed sometimes causes problem like that. If you have two strips of 256mb DDR, you may move it to different memory slots. First you may try single strip and see if the problem goes awy. If not, try 2 strips in 1&2, 1&3 or 2&3. Hope this will help.
You have a great system, it should work well. I have a Gigabyte motherboard also, 8IEXP, with 768MB of PC2100 (266MHz)DDR, Liteon LTD163 DVD, Liteon LTR48125W and overclocked Khypermedia (Benq) 48X to 52X burners, 1 IBM 36g and 2 18g Ultra SCSI160 hard drives. I am running WinXP without SP1.
Your problem may be caused by SP1 or the speed of the memory. I am not sure your motherboard will support DDR 400 ram, Anyway, good luck with your trouble shooting.
The fastest computer is not necessary a good running computer.