Hi M13,
Something is deffinetly wrong, whether it be a software or hardware!
I'd agree with that, please try a known constant, such as COD4, Crysis or even one of the popular gaming benchmark programs, and report back on performance, if they perform poorly too, then you definitely have a problem and we have a good grounding in which to help you better.
Also, do go through Nicks FSX OS guide in as far as it relates to your hardware and software, it's a gem of a guide if you follow it properly and dont cut corners.