Well, as this game was released waaay too early the min. requirements are ay more or less, educated guess.
But it was stated that todays "high-end" computers could run it a medium settings.
If you compare your rig with a actual "high-end" rig it is rather lower "med-end"
The min. requirements are plain wrong, but then, to really enjoy any demanding software you have to upgrade anyway.
I believe a higher "med-end" graphic-card with at least 1 gig vram and a bit overclocking your cpu would help a lot.
And for disappointment, i am not, but then i dont race against a F1 racer in a vw-beetle either