I'm going to say it's NOT a bottleneck issue, it's a driver or hardware compatibility issue... I'd start by booting from a Memtest CD and let it cycle for 2 hours to ensure there are no glaring hardware issues to contend with. If you have anything overclocked, un-do it for now and run all of your components in their factory specified configuration.
Did you install drivers from the supplied CD's or did you download mainboard chipset / video / etc.. drivers from the web to get the latest versions?
Get your chipset drivers here:
http://www.viaarena.com/default.aspx?PageID=420&OSID=1&CatID=1070
Get your current video driver from
www.nvidia.com
Besides the basic Windows XP and driver load, what applications do you have installed? In particular, anything that would prevent registry changes or software installation activities (a virus/spyware tool, etc..)? Have you verified in the System / Control panel / Device Manager / ATA controller devices, under the advanced settings tab, that your drives are utilizing DMA mode and not PIO?
Try all of that and let us know if anything seems to have an impact, good luck!